From cb4d48f53b1ce4aa0949623cc86b349cb300f534 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Fri, 13 Sep 2019 15:10:01 -0600
Subject: [PATCH 01/25] First attempt at quiver plot.

---
 xarray/plot/dataset_plot.py | 39 +++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index 6d942e1b0fa..8a4bba912d5 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -170,6 +170,8 @@ def _dsplot(plotfunc):
     ds : Dataset
     x, y : str
         Variable names for x, y axis.
+    u, v : string
+        Variable names for quiver plots
     hue: str, optional
         Variable by which to color scattered points
     hue_style: str, optional
@@ -250,6 +252,8 @@ def newplotfunc(
         ds,
         x=None,
         y=None,
+        u=None,
+        v=None,
         hue=None,
         hue_style=None,
         col=None,
@@ -321,9 +325,11 @@ def newplotfunc(
             ds=ds,
             x=x,
             y=y,
+            ax=ax,
+            u=u,
+            v=v,
             hue=hue,
             hue_style=hue_style,
-            ax=ax,
             cmap_params=cmap_params_subset,
             **kwargs,
         )
@@ -351,6 +357,8 @@ def plotmethod(
         _PlotMethods_obj,
         x=None,
         y=None,
+        u=None,
+        v=None,
         hue=None,
         hue_style=None,
         col=None,
@@ -398,7 +406,34 @@ def plotmethod(
 
 
 @_dsplot
-def scatter(ds, x, y, ax, **kwargs):
+def quiver(ds, x, y, ax, u, v, **kwargs):
+    if x is None or y is None or u is None or v is None:
+        raise ValueError("Must specify x, y, u, v for quiver plots.")
+
+    x, y, u, v = broadcast(ds[x], ds[y], ds[u], ds[v])
+
+    kwargs.pop("cmap_params")
+    kwargs.pop("hue")
+    kwargs.pop("hue_style")
+    hdl = ax.quiver(x.values, y.values, u.values, v.values, **kwargs)
+
+    # if plotfunc.__name__ == "quiver":
+    #         trans = ax._set_transform()
+    #         span, _y = trans.inverted().transform_point(
+    #             (ax.bbox.width, ax.bbox.height))
+    #         # matplotlib autoscaling algorithm
+    #         scale = kwargs.pop("scale")
+    #         if scale is None:
+    #             npts = ds.dims[x] * ds.dims[y]
+    #             # crude auto-scaling
+    #             # scale is typical arrow length as a multiple of the arrow width
+    #             scale = 1.8 * ds.mean() * np.max(10, np.sqrt(npts)) / span
+
+    return hdl
+
+
+@_dsplot
+def scatter(ds, x, y, ax, u, v, **kwargs):
     """
     Scatter Dataset data variables against each other.
     """

From fbca40ea2ca936a9211e5243398ec013864dbfd6 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 13:25:21 -0600
Subject: [PATCH 02/25] Support for quiver key

---
 xarray/plot/dataset_plot.py | 32 +++++++++++++++++++++++++++++---
 xarray/plot/facetgrid.py    | 27 ++++++++++++++++++++++++++-
 2 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index 8a4bba912d5..5f4af6f9c2e 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -1,5 +1,6 @@
 import functools
 
+import matplotlib as mpl
 import numpy as np
 import pandas as pd
 
@@ -17,7 +18,7 @@
 _MARKERSIZE_RANGE = np.array([18.0, 72.0])
 
 
-def _infer_meta_data(ds, x, y, hue, hue_style, add_guide):
+def _infer_meta_data(ds, x, y, hue, hue_style, add_guide, funcname):
     dvars = set(ds.variables.keys())
     error_msg = " must be one of ({:s})".format(", ".join(dvars))
 
@@ -48,11 +49,16 @@ def _infer_meta_data(ds, x, y, hue, hue_style, add_guide):
             add_colorbar = False
             add_legend = False
     else:
-        if add_guide is True:
+        if add_guide is True and funcname != "quiver":
             raise ValueError("Cannot set add_guide when hue is None.")
         add_legend = False
         add_colorbar = False
 
+    if (add_guide or add_guide is None) and funcname == "quiver":
+        add_quiverkey = True
+    else:
+        add_quiverkey = False
+
     if hue_style is not None and hue_style not in ["discrete", "continuous"]:
         raise ValueError("hue_style must be either None, 'discrete' or 'continuous'.")
 
@@ -66,6 +72,7 @@ def _infer_meta_data(ds, x, y, hue, hue_style, add_guide):
     return {
         "add_colorbar": add_colorbar,
         "add_legend": add_legend,
+        "add_quiverkey": add_quiverkey,
         "hue_label": hue_label,
         "hue_style": hue_style,
         "xlabel": label_from_attrs(ds[x]),
@@ -286,7 +293,9 @@ def newplotfunc(
         if _is_facetgrid:  # facetgrid call
             meta_data = kwargs.pop("meta_data")
         else:
-            meta_data = _infer_meta_data(ds, x, y, hue, hue_style, add_guide)
+            meta_data = _infer_meta_data(
+                ds, x, y, hue, hue_style, add_guide, funcname=plotfunc.__name__
+            )
 
         hue_style = meta_data["hue_style"]
 
@@ -350,6 +359,23 @@ def newplotfunc(
                 cbar_kwargs["label"] = meta_data.get("hue_label", None)
             _add_colorbar(primitive, ax, cbar_ax, cbar_kwargs, cmap_params)
 
+        if meta_data["add_quiverkey"]:
+            ticker = mpl.ticker.MaxNLocator(3)
+            median = np.median(np.hypot(ds[u].values, ds[v].values))
+            magnitude = ticker.tick_values(0, median)[-2]
+            units = ds[u].attrs.get("units", "")
+            ax.quiverkey(
+                primitive,
+                X=0.85,
+                Y=0.9,
+                U=magnitude,
+                label=f"{magnitude}\n{units}",
+                labelpos="E",
+                coordinates="figure",
+            )
+
+        ax.set_title(ds[u]._title_for_slice())
+
         return primitive
 
     @functools.wraps(newplotfunc)
diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index 58b38251352..d251df2cb5b 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -2,6 +2,7 @@
 import itertools
 import warnings
 
+import matplotlib as mpl
 import numpy as np
 
 from ..core.formatting import format_item
@@ -334,7 +335,9 @@ def map_dataset(
                 self.data[kwargs["markersize"]], kwargs.pop("size_norm", None)
             )
 
-        meta_data = _infer_meta_data(self.data, x, y, hue, hue_style, add_guide)
+        meta_data = _infer_meta_data(
+            self.data, x, y, hue, hue_style, add_guide, funcname=func.__name__
+        )
         kwargs["meta_data"] = meta_data
 
         if hue and meta_data["hue_style"] == "continuous":
@@ -365,6 +368,9 @@ def map_dataset(
             elif meta_data["add_colorbar"]:
                 self.add_colorbar(label=self._hue_label, **cbar_kwargs)
 
+        if meta_data["add_quiverkey"]:
+            self.add_quiverkey(kwargs["u"], kwargs["v"])
+
         return self
 
     def _finalize_grid(self, *axlabels):
@@ -426,6 +432,25 @@ def add_colorbar(self, **kwargs):
         )
         return self
 
+    def add_quiverkey(self, u, v, **kwargs):
+        kwargs = kwargs.copy()
+
+        ticker = mpl.ticker.MaxNLocator(3)
+        median = np.median(np.hypot(self.data[u].values, self.data[v].values))
+        magnitude = ticker.tick_values(0, median)[-2]
+        units = self.data[u].attrs.get("units", "")
+        self.axes.flat[-1].quiverkey(
+            self._mappables[-1],
+            X=0.95,
+            Y=0.9,
+            U=magnitude,
+            label=f"{magnitude}\n{units}",
+            labelpos="E",
+            coordinates="figure",
+        )
+
+        return self
+
     def set_axis_labels(self, x_var=None, y_var=None):
         """Set axis labels on the left column and bottom row of the grid."""
         if x_var is not None:

From fc8ad67cf4ee5381de0b9e58d607b190ca63798c Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 14:12:03 -0600
Subject: [PATCH 03/25] refactor out adjusting subplots for legend

---
 xarray/plot/facetgrid.py | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index d251df2cb5b..fc123a9eba0 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -386,30 +386,22 @@ def _finalize_grid(self, *axlabels):
 
             self._finalized = True
 
-    def add_legend(self, **kwargs):
-        figlegend = self.fig.legend(
-            handles=self._mappables[-1],
-            labels=list(self._hue_var.values),
-            title=self._hue_label,
-            loc="center right",
-            **kwargs,
-        )
-
-        self.figlegend = figlegend
+    def _adjust_fig_for_guide(self, guide):
         # Draw the plot to set the bounding boxes correctly
-        self.fig.draw(self.fig.canvas.get_renderer())
+        renderer = self.fig.canvas.get_renderer()
+        self.fig.draw(renderer)
 
         # Calculate and set the new width of the figure so the legend fits
-        legend_width = figlegend.get_window_extent().width / self.fig.dpi
+        guide_width = guide.get_window_extent(renderer).width / self.fig.dpi
         figure_width = self.fig.get_figwidth()
-        self.fig.set_figwidth(figure_width + legend_width)
+        self.fig.set_figwidth(figure_width + guide_width)
 
         # Draw the plot again to get the new transformations
-        self.fig.draw(self.fig.canvas.get_renderer())
+        self.fig.draw(renderer)
 
         # Now calculate how much space we need on the right side
-        legend_width = figlegend.get_window_extent().width / self.fig.dpi
-        space_needed = legend_width / (figure_width + legend_width) + 0.02
+        guide_width = guide.get_window_extent(renderer).width / self.fig.dpi
+        space_needed = guide_width / (figure_width + guide_width) + 0.02
         # margin = .01
         # _space_needed = margin + space_needed
         right = 1 - space_needed
@@ -417,6 +409,16 @@ def add_legend(self, **kwargs):
         # Place the subplot axes to give space for the legend
         self.fig.subplots_adjust(right=right)
 
+    def add_legend(self, **kwargs):
+        self.figlegend = self.fig.legend(
+            handles=self._mappables[-1],
+            labels=list(self._hue_var.values),
+            title=self._hue_label,
+            loc="center right",
+            **kwargs,
+        )
+        self._adjust_fig_for_guide(self.figlegend)
+
     def add_colorbar(self, **kwargs):
         """Draw a colorbar"""
         kwargs = kwargs.copy()

From 190d788d89ee59780f13912d063b57087be2f92c Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 14:12:17 -0600
Subject: [PATCH 04/25] Adjust figure for quiverkey.

This does not work because quiverkey.get_window_extent(...) return 0...
---
 xarray/plot/facetgrid.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index fc123a9eba0..ce54c59d31d 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -441,16 +441,18 @@ def add_quiverkey(self, u, v, **kwargs):
         median = np.median(np.hypot(self.data[u].values, self.data[v].values))
         magnitude = ticker.tick_values(0, median)[-2]
         units = self.data[u].attrs.get("units", "")
-        self.axes.flat[-1].quiverkey(
+        self.quiverkey = self.axes.flat[-1].quiverkey(
             self._mappables[-1],
             X=0.95,
-            Y=0.9,
+            Y=0.5,
             U=magnitude,
             label=f"{magnitude}\n{units}",
             labelpos="E",
             coordinates="figure",
         )
 
+        self._adjust_fig_for_guide(self.quiverkey)
+
         return self
 
     def set_axis_labels(self, x_var=None, y_var=None):

From 51cb73e93cc4f2dbc7565bec7c47375de207d06a Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 15:01:15 -0600
Subject: [PATCH 05/25] Update quiverkey

---
 xarray/plot/dataset_plot.py |  6 ++----
 xarray/plot/facetgrid.py    | 18 +++++++++---------
 xarray/plot/utils.py        |  9 +++++++++
 3 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index 5f4af6f9c2e..57b544b69cf 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -1,6 +1,5 @@
 import functools
 
-import matplotlib as mpl
 import numpy as np
 import pandas as pd
 
@@ -8,6 +7,7 @@
 from .facetgrid import _easy_facetgrid
 from .utils import (
     _add_colorbar,
+    _get_nice_quiver_magnitude,
     _is_numeric,
     _process_cmap_cbar_kwargs,
     get_axis,
@@ -360,9 +360,7 @@ def newplotfunc(
             _add_colorbar(primitive, ax, cbar_ax, cbar_kwargs, cmap_params)
 
         if meta_data["add_quiverkey"]:
-            ticker = mpl.ticker.MaxNLocator(3)
-            median = np.median(np.hypot(ds[u].values, ds[v].values))
-            magnitude = ticker.tick_values(0, median)[-2]
+            magnitude = _get_nice_quiver_magnitude(ds[u], ds[v])
             units = ds[u].attrs.get("units", "")
             ax.quiverkey(
                 primitive,
diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index ce54c59d31d..42044c30281 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -2,11 +2,11 @@
 import itertools
 import warnings
 
-import matplotlib as mpl
 import numpy as np
 
 from ..core.formatting import format_item
 from .utils import (
+    _get_nice_quiver_magnitude,
     _infer_xy_labels,
     _process_cmap_cbar_kwargs,
     import_matplotlib_pyplot,
@@ -328,7 +328,6 @@ def map_dataset(
         from .dataset_plot import _infer_meta_data, _parse_size
 
         kwargs["add_guide"] = False
-        kwargs["_is_facetgrid"] = True
 
         if kwargs.get("markersize", None):
             kwargs["size_mapping"] = _parse_size(
@@ -347,6 +346,8 @@ def map_dataset(
             kwargs["meta_data"]["cmap_params"] = cmap_params
             kwargs["meta_data"]["cbar_kwargs"] = cbar_kwargs
 
+        kwargs["_is_facetgrid"] = True
+
         for d, ax in zip(self.name_dicts.flat, self.axes.flat):
             # None is the sentinel value
             if d is not None:
@@ -437,21 +438,20 @@ def add_colorbar(self, **kwargs):
     def add_quiverkey(self, u, v, **kwargs):
         kwargs = kwargs.copy()
 
-        ticker = mpl.ticker.MaxNLocator(3)
-        median = np.median(np.hypot(self.data[u].values, self.data[v].values))
-        magnitude = ticker.tick_values(0, median)[-2]
+        magnitude = _get_nice_quiver_magnitude(self.data[u], self.data[v])
         units = self.data[u].attrs.get("units", "")
         self.quiverkey = self.axes.flat[-1].quiverkey(
             self._mappables[-1],
-            X=0.95,
-            Y=0.5,
+            X=0.85,
+            Y=1.03,
             U=magnitude,
             label=f"{magnitude}\n{units}",
             labelpos="E",
-            coordinates="figure",
+            coordinates="axes",
         )
 
-        self._adjust_fig_for_guide(self.quiverkey)
+        # TODO: does not work because self.quiverkey.get_window_extent(renderer) = 0
+        # self._adjust_fig_for_guide(self.quiverkey)
 
         return self
 
diff --git a/xarray/plot/utils.py b/xarray/plot/utils.py
index 16c67e154fc..278ed964073 100644
--- a/xarray/plot/utils.py
+++ b/xarray/plot/utils.py
@@ -840,3 +840,12 @@ def _process_cmap_cbar_kwargs(
         }
 
     return cmap_params, cbar_kwargs
+
+
+def _get_nice_quiver_magnitude(u, v):
+    import matplotlib as mpl
+
+    ticker = mpl.ticker.MaxNLocator(3)
+    median = np.median(np.hypot(u.values, v.values))
+    magnitude = ticker.tick_values(0, median)[-2]
+    return magnitude

From 9cb6a61afbced13b4c0123573d70e69ca295af6c Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 15:01:31 -0600
Subject: [PATCH 06/25] Autoscale quiver facetgrid

---
 xarray/plot/facetgrid.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index 42044c30281..20d1b214e7c 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -348,6 +348,21 @@ def map_dataset(
 
         kwargs["_is_facetgrid"] = True
 
+        if func.__name__ == "quiver" and "scale" not in kwargs:
+            if "scale_units" in kwargs and kwargs["scale_units"] is not None:
+                raise NotImplementedError("Can't pass only scale_units.")
+            # autoscaling
+            ax = self.axes[0, 0]
+            magnitude = _get_nice_quiver_magnitude(
+                self.data[kwargs["u"]], self.data[kwargs["v"]]
+            )
+            # matplotlib autoscaling algorithm
+            span = ax.get_transform().inverted().transform_bbox(ax.bbox).width
+            npts = self.data.sizes[x] * self.data.sizes[y]
+            # scale is typical arrow length as a multiple of the arrow width
+            scale = 1.8 * magnitude * max(10, np.sqrt(npts)) / span
+            kwargs["scale"] = 1 / scale  # TODO: why?
+
         for d, ax in zip(self.name_dicts.flat, self.axes.flat):
             # None is the sentinel value
             if d is not None:

From c2dcc1d760dc4617057f7dcd62979363363e4ede Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 15:01:43 -0600
Subject: [PATCH 07/25] Support for hue

---
 xarray/plot/dataset_plot.py | 39 ++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index 57b544b69cf..7a48d7e7870 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -56,6 +56,14 @@ def _infer_meta_data(ds, x, y, hue, hue_style, add_guide, funcname):
 
     if (add_guide or add_guide is None) and funcname == "quiver":
         add_quiverkey = True
+        if hue:
+            add_colorbar = True
+            if not hue_style:
+                hue_style = "continuous"
+            elif hue_style != "continuous":
+                raise ValueError(
+                    "hue_style must be 'continuous' or None for .plot.quiver"
+                )
     else:
         add_quiverkey = False
 
@@ -431,28 +439,27 @@ def plotmethod(
 
 @_dsplot
 def quiver(ds, x, y, ax, u, v, **kwargs):
+    import matplotlib as mpl
+
     if x is None or y is None or u is None or v is None:
         raise ValueError("Must specify x, y, u, v for quiver plots.")
 
     x, y, u, v = broadcast(ds[x], ds[y], ds[u], ds[v])
 
-    kwargs.pop("cmap_params")
-    kwargs.pop("hue")
-    kwargs.pop("hue_style")
-    hdl = ax.quiver(x.values, y.values, u.values, v.values, **kwargs)
-
-    # if plotfunc.__name__ == "quiver":
-    #         trans = ax._set_transform()
-    #         span, _y = trans.inverted().transform_point(
-    #             (ax.bbox.width, ax.bbox.height))
-    #         # matplotlib autoscaling algorithm
-    #         scale = kwargs.pop("scale")
-    #         if scale is None:
-    #             npts = ds.dims[x] * ds.dims[y]
-    #             # crude auto-scaling
-    #             # scale is typical arrow length as a multiple of the arrow width
-    #             scale = 1.8 * ds.mean() * np.max(10, np.sqrt(npts)) / span
+    args = [x.values, y.values, u.values, v.values]
+    hue = kwargs.pop("hue")
+    if hue:
+        args.append(ds[hue].values)
 
+    # TODO: Fix this by always returning a norm with vmin, vmax in cmap_params
+    cmap_params = kwargs.pop("cmap_params")
+    if not cmap_params["norm"]:
+        cmap_params["norm"] = mpl.colors.Normalize(
+            cmap_params.pop("vmin"), cmap_params.pop("vmax")
+        )
+
+    kwargs.pop("hue_style")
+    hdl = ax.quiver(*args, **kwargs, **cmap_params)
     return hdl
 
 

From 0393e66602d84391d0b5746c89077e9c94ed1a86 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 16:23:55 -0600
Subject: [PATCH 08/25] fix tests.

---
 xarray/tests/test_plot.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index 47b15446f1d..549a3c49c1f 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -2194,7 +2194,13 @@ def test_accessor(self):
     def test_add_guide(self, add_guide, hue_style, legend, colorbar):
 
         meta_data = _infer_meta_data(
-            self.ds, x="A", y="B", hue="hue", hue_style=hue_style, add_guide=add_guide
+            self.ds,
+            x="A",
+            y="B",
+            hue="hue",
+            hue_style=hue_style,
+            add_guide=add_guide,
+            funcname="scatter",
         )
         assert meta_data["add_legend"] is legend
         assert meta_data["add_colorbar"] is colorbar

From 8116ec95c98505eaf79ee87ba18226dd8b1ea2d3 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 5 Sep 2020 16:28:52 -0600
Subject: [PATCH 09/25] Fix test

---
 xarray/plot/dataset_plot.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index 7a48d7e7870..1aabb218df7 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -380,7 +380,11 @@ def newplotfunc(
                 coordinates="figure",
             )
 
-        ax.set_title(ds[u]._title_for_slice())
+        if plotfunc.__name__ == "quiver":
+            title = ds[u]._title_for_slice()
+        else:
+            title = ds[x]._title_for_slice()
+        ax.set_title(title)
 
         return primitive
 

From 04f64c562be7f7ffd25c34f1991da5f1d6cf3ba9 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 19 Sep 2020 18:03:36 -0600
Subject: [PATCH 10/25] Adding docs

---
 doc/plotting.rst | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/doc/plotting.rst b/doc/plotting.rst
index 3699f794ae8..767a4ca58cd 100644
--- a/doc/plotting.rst
+++ b/doc/plotting.rst
@@ -715,6 +715,9 @@ Consider this dataset
     ds
 
 
+Scatter
+~~~~~~~
+
 Suppose we want to scatter ``A`` against ``B``
 
 .. ipython:: python
@@ -762,6 +765,24 @@ Faceting is also possible
 
 For more advanced scatter plots, we recommend converting the relevant data variables to a pandas DataFrame and using the extensive plotting capabilities of ``seaborn``.
 
+Quiver
+~~~~~~
+
+.. ipython:: python
+    :okwarning:
+
+    @savefig ds_simple_quiver.png
+    ds.isel(w=1, z=1).plot.quiver(x="x", y="y", u="A", v="B")
+
+
+Again, faceting is also possible
+
+.. ipython:: python
+    :okwarning:
+
+    @savefig ds_facet_quiver.png
+    ds.plot.quiver(x="x", y="y", u="A", v="B", col="w", row="z", scale=4)
+
 
 .. _plot-maps:
 

From abcc0081a4c37b60dfb35653301f47cebce0029b Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sat, 19 Sep 2020 18:03:59 -0600
Subject: [PATCH 11/25] small fixes

---
 xarray/plot/dataset_plot.py | 54 +++++++++++++++++++------------------
 xarray/plot/facetgrid.py    | 39 ++++++++++++++-------------
 xarray/plot/utils.py        |  2 +-
 3 files changed, 50 insertions(+), 45 deletions(-)

diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index 1aabb218df7..a9a4cd54d3b 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -441,32 +441,6 @@ def plotmethod(
     return newplotfunc
 
 
-@_dsplot
-def quiver(ds, x, y, ax, u, v, **kwargs):
-    import matplotlib as mpl
-
-    if x is None or y is None or u is None or v is None:
-        raise ValueError("Must specify x, y, u, v for quiver plots.")
-
-    x, y, u, v = broadcast(ds[x], ds[y], ds[u], ds[v])
-
-    args = [x.values, y.values, u.values, v.values]
-    hue = kwargs.pop("hue")
-    if hue:
-        args.append(ds[hue].values)
-
-    # TODO: Fix this by always returning a norm with vmin, vmax in cmap_params
-    cmap_params = kwargs.pop("cmap_params")
-    if not cmap_params["norm"]:
-        cmap_params["norm"] = mpl.colors.Normalize(
-            cmap_params.pop("vmin"), cmap_params.pop("vmax")
-        )
-
-    kwargs.pop("hue_style")
-    hdl = ax.quiver(*args, **kwargs, **cmap_params)
-    return hdl
-
-
 @_dsplot
 def scatter(ds, x, y, ax, u, v, **kwargs):
     """
@@ -520,3 +494,31 @@ def scatter(ds, x, y, ax, u, v, **kwargs):
         )
 
     return primitive
+
+
+@_dsplot
+def quiver(ds, x, y, ax, u, v, **kwargs):
+    import matplotlib as mpl
+
+    if x is None or y is None or u is None or v is None:
+        raise ValueError("Must specify x, y, u, v for quiver plots.")
+
+    x, y, u, v = broadcast(ds[x], ds[y], ds[u], ds[v])
+
+    args = [x.values, y.values, u.values, v.values]
+    hue = kwargs.pop("hue")
+    cmap_params = kwargs.pop("cmap_params")
+
+    if hue:
+        args.append(ds[hue].values)
+
+        # TODO: Fix this by always returning a norm with vmin, vmax in cmap_params
+        if not cmap_params["norm"]:
+            cmap_params["norm"] = mpl.colors.Normalize(
+                cmap_params.pop("vmin"), cmap_params.pop("vmax")
+            )
+
+    kwargs.pop("hue_style")
+    kwargs.setdefault("pivot", "middle")
+    hdl = ax.quiver(*args, **kwargs, **cmap_params)
+    return hdl
diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index 20d1b214e7c..0e03f56670c 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -349,19 +349,22 @@ def map_dataset(
         kwargs["_is_facetgrid"] = True
 
         if func.__name__ == "quiver" and "scale" not in kwargs:
-            if "scale_units" in kwargs and kwargs["scale_units"] is not None:
-                raise NotImplementedError("Can't pass only scale_units.")
-            # autoscaling
-            ax = self.axes[0, 0]
-            magnitude = _get_nice_quiver_magnitude(
-                self.data[kwargs["u"]], self.data[kwargs["v"]]
-            )
-            # matplotlib autoscaling algorithm
-            span = ax.get_transform().inverted().transform_bbox(ax.bbox).width
-            npts = self.data.sizes[x] * self.data.sizes[y]
-            # scale is typical arrow length as a multiple of the arrow width
-            scale = 1.8 * magnitude * max(10, np.sqrt(npts)) / span
-            kwargs["scale"] = 1 / scale  # TODO: why?
+            raise ValueError("Please provide scale.")
+            # TODO: come up with an algorithm for reasonable scale choice
+            # if "scale_units" in kwargs and kwargs["scale_units"] is not None:
+            #     raise NotImplementedError("Can't pass only scale_units.")
+            # # autoscaling
+            # ax = self.axes[0, 0]
+            # magnitude = _get_nice_quiver_magnitude(
+            #     self.data[kwargs["u"]], self.data[kwargs["v"]]
+            # )
+            # # matplotlib autoscaling algorithm
+            # span = ax.get_transform().inverted().transform_bbox(ax.bbox).width
+            # npts = self.data.sizes[x] * self.data.sizes[y]
+            # # scale is typical arrow length as a multiple of the arrow width
+            # print(magnitude, np.sqrt(npts), span)
+            # kwargs["scale"] = 1.8 * magnitude * min(10, np.sqrt(npts)) / span
+            # print(kwargs["scale"])
 
         for d, ax in zip(self.name_dicts.flat, self.axes.flat):
             # None is the sentinel value
@@ -457,17 +460,17 @@ def add_quiverkey(self, u, v, **kwargs):
         units = self.data[u].attrs.get("units", "")
         self.quiverkey = self.axes.flat[-1].quiverkey(
             self._mappables[-1],
-            X=0.85,
-            Y=1.03,
+            X=0.8,
+            Y=0.9,
             U=magnitude,
             label=f"{magnitude}\n{units}",
             labelpos="E",
-            coordinates="axes",
+            coordinates="figure",
         )
 
         # TODO: does not work because self.quiverkey.get_window_extent(renderer) = 0
-        # self._adjust_fig_for_guide(self.quiverkey)
-
+        # https://github.com/matplotlib/matplotlib/issues/18530
+        # self._adjust_fig_for_guide(self.quiverkey.text)
         return self
 
     def set_axis_labels(self, x_var=None, y_var=None):
diff --git a/xarray/plot/utils.py b/xarray/plot/utils.py
index 278ed964073..adb60c628d7 100644
--- a/xarray/plot/utils.py
+++ b/xarray/plot/utils.py
@@ -846,6 +846,6 @@ def _get_nice_quiver_magnitude(u, v):
     import matplotlib as mpl
 
     ticker = mpl.ticker.MaxNLocator(3)
-    median = np.median(np.hypot(u.values, v.values))
+    median = np.mean(np.hypot(u.values, v.values))
     magnitude = ticker.tick_values(0, median)[-2]
     return magnitude

From f1da0c0c28fa6b4599f880f102613aa92934eb46 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Thu, 8 Oct 2020 14:03:42 -0600
Subject: [PATCH 12/25] Start adding tests

---
 xarray/tests/test_plot.py | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index 549a3c49c1f..a83ac5635af 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -2152,6 +2152,29 @@ def test_wrong_num_of_dimensions(self):
             self.darray.plot.line(row="row", hue="hue")
 
 
+@requires_matplotlib
+class TestDatasetQuiverPlots(PlotTestCase):
+    @pytest.fixture(autouse=True)
+    def setUp(self):
+        das = [
+            DataArray(
+                np.random.randn(3, 3, 4, 4),
+                dims=["x", "row", "col", "hue"],
+                coords=[range(k) for k in [3, 3, 4, 4]],
+            )
+            for _ in [1, 2]
+        ]
+        ds = Dataset({"A": das[0], "B": das[1]})
+        ds.hue.name = "huename"
+        ds.hue.attrs["units"] = "hunits"
+        ds.x.attrs["units"] = "xunits"
+        ds.col.attrs["units"] = "colunits"
+        ds.row.attrs["units"] = "rowunits"
+        ds.A.attrs["units"] = "Aunits"
+        ds.B.attrs["units"] = "Bunits"
+        self.ds = ds
+
+
 @requires_matplotlib
 class TestDatasetScatterPlots(PlotTestCase):
     @pytest.fixture(autouse=True)

From 39545b1aa0f7d901b093961c1193de0bfb871ebf Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Tue, 19 Jan 2021 17:14:14 -0700
Subject: [PATCH 13/25] Simple tests.

---
 xarray/tests/test_plot.py | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index a83ac5635af..d3aade4d0bf 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -2159,21 +2159,38 @@ def setUp(self):
         das = [
             DataArray(
                 np.random.randn(3, 3, 4, 4),
-                dims=["x", "row", "col", "hue"],
+                dims=["x", "y", "row", "col"],
                 coords=[range(k) for k in [3, 3, 4, 4]],
             )
             for _ in [1, 2]
         ]
-        ds = Dataset({"A": das[0], "B": das[1]})
-        ds.hue.name = "huename"
-        ds.hue.attrs["units"] = "hunits"
+        ds = Dataset({"u": das[0], "v": das[1]})
         ds.x.attrs["units"] = "xunits"
+        ds.y.attrs["units"] = "yunits"
         ds.col.attrs["units"] = "colunits"
         ds.row.attrs["units"] = "rowunits"
-        ds.A.attrs["units"] = "Aunits"
-        ds.B.attrs["units"] = "Bunits"
+        ds.u.attrs["units"] = "uunits"
+        ds.v.attrs["units"] = "vunits"
+        ds["mag"] = np.hypot(ds.u, ds.v)
         self.ds = ds
 
+    def test_quiver(self):
+        with figure_context():
+            hdl = self.ds.isel(row=0, col=0).plot.quiver(x="x", y="y", u="u", v="v")
+            assert isinstance(hdl, mpl.quiver.Quiver)
+        with raises_regex(ValueError, "specify x, y, u, v"):
+            self.ds.isel(row=0, col=0).plot.quiver(x="x", y="y", u="u")
+
+    def test_facetgrid(self):
+        with figure_context():
+            fg = self.ds.plot.quiver(
+                x="x", y="y", u="u", v="v", row="row", col="col", scale=1, hue="mag"
+            )
+            for handle in fg._mappables:
+                assert isinstance(handle, mpl.quiver.Quiver)
+        with raises_regex(ValueError, "Please provide scale"):
+            self.ds.plot.quiver(x="x", y="y", u="u", v="v", row="row", col="col")
+
 
 @requires_matplotlib
 class TestDatasetScatterPlots(PlotTestCase):

From b6c1bc81a17a27c360211dac23f8086c3fe22183 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Tue, 19 Jan 2021 17:21:36 -0700
Subject: [PATCH 14/25] [skip-ci] Start adding docs.

---
 doc/api.rst                 | 1 +
 xarray/plot/dataset_plot.py | 1 +
 2 files changed, 2 insertions(+)

diff --git a/doc/api.rst b/doc/api.rst
index ceab7dcc976..ce866093db8 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -240,6 +240,7 @@ Plotting
    :template: autosummary/accessor_method.rst
 
    Dataset.plot.scatter
+   Dataset.plot.quiver
 
 DataArray
 =========
diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index a9a4cd54d3b..fb850be0641 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -498,6 +498,7 @@ def scatter(ds, x, y, ax, u, v, **kwargs):
 
 @_dsplot
 def quiver(ds, x, y, ax, u, v, **kwargs):
+    """ Quiver plot with Dataset variables."""
     import matplotlib as mpl
 
     if x is None or y is None or u is None or v is None:

From 7b559453a88eb1fc2b425b3dd3d54e295674006c Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Tue, 19 Jan 2021 17:25:26 -0700
Subject: [PATCH 15/25] [skip-ci] add whats-new

---
 doc/whats-new.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 88994a5bfc0..502181487b9 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -47,6 +47,8 @@ New Features
 ~~~~~~~~~~~~
 - Performance improvement when constructing DataArrays. Significantly speeds up repr for Datasets with large number of variables.
   By `Deepak Cherian <https://github.com/dcherian>`_
+- Add :py:meth:`Dataset.plot.quiver` for quiver plots with :py:class:`Dataset` variables.
+  By `Deepak Cherian <https://github.com/dcherian>`_
 
 Bug fixes
 ~~~~~~~~~

From 0da3540161ec6a1cac17caa4fa40ea2442636d45 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Wed, 20 Jan 2021 11:44:54 -0700
Subject: [PATCH 16/25] Add quiverkey test

---
 xarray/plot/facetgrid.py  |  4 ++++
 xarray/tests/test_plot.py | 15 +++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index 0e03f56670c..95be05a4a25 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -196,7 +196,11 @@ def __init__(
         self.axes = axes
         self.row_names = row_names
         self.col_names = col_names
+
+        # guides
         self.figlegend = None
+        self.quiverkey = None
+        self.cbar = None
 
         # Next the private variables
         self._single_group = single_group
diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index d3aade4d0bf..c1201782791 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -2188,6 +2188,21 @@ def test_facetgrid(self):
             )
             for handle in fg._mappables:
                 assert isinstance(handle, mpl.quiver.Quiver)
+            assert "uunits" in fg.quiverkey.text.get_text()
+
+        with figure_context():
+            fg = self.ds.plot.quiver(
+                x="x",
+                y="y",
+                u="u",
+                v="v",
+                row="row",
+                col="col",
+                scale=1,
+                hue="mag",
+                add_guide=False,
+            )
+            assert fg.quiverkey is None
         with raises_regex(ValueError, "Please provide scale"):
             self.ds.plot.quiver(x="x", y="y", u="u", v="v", row="row", col="col")
 

From bc785826af6ba0b6ae728acc02f5cbac2382012d Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Wed, 20 Jan 2021 11:48:05 -0700
Subject: [PATCH 17/25] Add test for hue_style

---
 xarray/tests/test_plot.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index c1201782791..d8bf6632914 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -2181,6 +2181,11 @@ def test_quiver(self):
         with raises_regex(ValueError, "specify x, y, u, v"):
             self.ds.isel(row=0, col=0).plot.quiver(x="x", y="y", u="u")
 
+        with raises_regex(ValueError, "hue_style"):
+            self.ds.isel(row=0, col=0).plot.quiver(
+                x="x", y="y", u="u", hue_style="discrete"
+            )
+
     def test_facetgrid(self):
         with figure_context():
             fg = self.ds.plot.quiver(

From d1e028ccbb3adbad20bce423bf7d95b07cf5905e Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Wed, 20 Jan 2021 11:50:20 -0700
Subject: [PATCH 18/25] small doc updates.

---
 doc/plotting.rst            | 2 ++
 xarray/plot/dataset_plot.py | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/doc/plotting.rst b/doc/plotting.rst
index 767a4ca58cd..a6866f98b11 100644
--- a/doc/plotting.rst
+++ b/doc/plotting.rst
@@ -768,6 +768,8 @@ For more advanced scatter plots, we recommend converting the relevant data varia
 Quiver
 ~~~~~~
 
+Visualizing vector fields using a quiver plot is easy.
+
 .. ipython:: python
     :okwarning:
 
diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index fb850be0641..e71091eb9cb 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -185,7 +185,7 @@ def _dsplot(plotfunc):
     ds : Dataset
     x, y : str
         Variable names for x, y axis.
-    u, v : string
+    u, v : str, optional
         Variable names for quiver plots
     hue: str, optional
         Variable by which to color scattered points

From 94f83969379ce19981c5365a2198183b05dee2a4 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Wed, 20 Jan 2021 11:50:55 -0700
Subject: [PATCH 19/25] remove commented out autoscaling code

---
 xarray/plot/facetgrid.py | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/xarray/plot/facetgrid.py b/xarray/plot/facetgrid.py
index 95be05a4a25..cf76000e806 100644
--- a/xarray/plot/facetgrid.py
+++ b/xarray/plot/facetgrid.py
@@ -355,20 +355,6 @@ def map_dataset(
         if func.__name__ == "quiver" and "scale" not in kwargs:
             raise ValueError("Please provide scale.")
             # TODO: come up with an algorithm for reasonable scale choice
-            # if "scale_units" in kwargs and kwargs["scale_units"] is not None:
-            #     raise NotImplementedError("Can't pass only scale_units.")
-            # # autoscaling
-            # ax = self.axes[0, 0]
-            # magnitude = _get_nice_quiver_magnitude(
-            #     self.data[kwargs["u"]], self.data[kwargs["v"]]
-            # )
-            # # matplotlib autoscaling algorithm
-            # span = ax.get_transform().inverted().transform_bbox(ax.bbox).width
-            # npts = self.data.sizes[x] * self.data.sizes[y]
-            # # scale is typical arrow length as a multiple of the arrow width
-            # print(magnitude, np.sqrt(npts), span)
-            # kwargs["scale"] = 1.8 * magnitude * min(10, np.sqrt(npts)) / span
-            # print(kwargs["scale"])
 
         for d, ax in zip(self.name_dicts.flat, self.axes.flat):
             # None is the sentinel value

From de48d51fe5a13e190404d08ed9cd6b2fda474716 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Wed, 20 Jan 2021 11:55:51 -0700
Subject: [PATCH 20/25] Raise if u,v are provided for non-quiver plots.

---
 xarray/plot/dataset_plot.py | 3 +++
 xarray/tests/test_plot.py   | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/xarray/plot/dataset_plot.py b/xarray/plot/dataset_plot.py
index e71091eb9cb..59d3ca98f23 100644
--- a/xarray/plot/dataset_plot.py
+++ b/xarray/plot/dataset_plot.py
@@ -338,6 +338,9 @@ def newplotfunc(
         else:
             cmap_params_subset = {}
 
+        if (u is not None or v is not None) and plotfunc.__name__ != "quiver":
+            raise ValueError("u, v are only allowed for quiver plots.")
+
         primitive = plotfunc(
             ds=ds,
             x=x,
diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index d8bf6632914..5f735a6769e 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -2339,6 +2339,9 @@ def test_facetgrid_hue_style(self):
     def test_scatter(self, x, y, hue, markersize):
         self.ds.plot.scatter(x, y, hue=hue, markersize=markersize)
 
+        with raises_regex(ValueError, "u, v"):
+            self.ds.plot.scatter(x, y, u="col", v="row")
+
     def test_non_numeric_legend(self):
         ds2 = self.ds.copy()
         ds2["hue"] = ["a", "b", "c", "d"]

From e795672b6dc01725ff0e7d7157fc1ec5d5cddf43 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Wed, 20 Jan 2021 14:12:35 -0700
Subject: [PATCH 21/25] Fix tests

---
 xarray/tests/test_plot.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index 5f735a6769e..705b2d5e2e7 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -1475,7 +1475,7 @@ def test_facetgrid_cbar_kwargs(self):
         )
 
         # catch contour case
-        if hasattr(g, "cbar"):
+        if g.cbar is not None:
             assert get_colorbar_label(g.cbar) == "test_label"
 
     def test_facetgrid_no_cbar_ax(self):
@@ -2183,7 +2183,7 @@ def test_quiver(self):
 
         with raises_regex(ValueError, "hue_style"):
             self.ds.isel(row=0, col=0).plot.quiver(
-                x="x", y="y", u="u", hue_style="discrete"
+                x="x", y="y", u="u", v="v", hue="mag", hue_style="discrete"
             )
 
     def test_facetgrid(self):

From 8a3912c7218e894ca2663d7fffceb146cdf93d9b Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Fri, 29 Jan 2021 16:28:20 -0700
Subject: [PATCH 22/25] [skip-ci] fix bad merge.

---
 doc/whats-new.rst | 1 -
 1 file changed, 1 deletion(-)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index bb81426e4dd..3ef8009ba86 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -60,7 +60,6 @@ New Features
 - Performance improvement when constructing DataArrays. Significantly speeds up repr for Datasets with large number of variables.
   By `Deepak Cherian <https://github.com/dcherian>`_
 - Add :py:meth:`Dataset.plot.quiver` for quiver plots with :py:class:`Dataset` variables.
-  By `Deepak Cherian <https://github.com/dcherian>`_
   By `Deepak Cherian <https://github.com/dcherian>`_.
 - :py:meth:`DataArray.swap_dims` & :py:meth:`Dataset.swap_dims` now accept dims
   in the form of kwargs as well as a dict, like most similar methods.

From ca00bd4d39d0fae8af35f446cfe0575eaa1d3f7f Mon Sep 17 00:00:00 2001
From: Deepak Cherian <dcherian@users.noreply.github.com>
Date: Wed, 10 Feb 2021 15:19:42 -0700
Subject: [PATCH 23/25] [skip-ci] update whats-new

---
 doc/whats-new.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 47c35458acb..9cdfe1517c4 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -145,7 +145,7 @@ Internal Changes
   the other ``assert_*`` functions (:pull:`4864`). By `Mathias Hauser <https://github.com/mathause>`_.
 - Performance improvement when constructing DataArrays. Significantly speeds up repr for Datasets with large number of variables.
   By `Deepak Cherian <https://github.com/dcherian>`_
-  
+
 .. _whats-new.0.16.2:
 
 v0.16.2 (30 Nov 2020)

From d2cf58c4c71cde14d2b86febdbe3f96428a06eec Mon Sep 17 00:00:00 2001
From: Deepak Cherian <dcherian@users.noreply.github.com>
Date: Fri, 12 Feb 2021 07:04:40 -0700
Subject: [PATCH 24/25] [skip-ci] Apply suggestions from code review

Co-authored-by: Mathias Hauser <mathause@users.noreply.github.com>
---
 doc/plotting.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/doc/plotting.rst b/doc/plotting.rst
index a6866f98b11..2ada3e25431 100644
--- a/doc/plotting.rst
+++ b/doc/plotting.rst
@@ -768,7 +768,7 @@ For more advanced scatter plots, we recommend converting the relevant data varia
 Quiver
 ~~~~~~
 
-Visualizing vector fields using a quiver plot is easy.
+Visualizing vector fields is supported with quiver plots:
 
 .. ipython:: python
     :okwarning:
@@ -777,7 +777,7 @@ Visualizing vector fields using a quiver plot is easy.
     ds.isel(w=1, z=1).plot.quiver(x="x", y="y", u="A", v="B")
 
 
-Again, faceting is also possible
+where ``u`` and ``v`` denote the x and y direction components of the arrow vectors. Again, faceting is also possible:
 
 .. ipython:: python
     :okwarning:
@@ -785,6 +785,7 @@ Again, faceting is also possible
     @savefig ds_facet_quiver.png
     ds.plot.quiver(x="x", y="y", u="A", v="B", col="w", row="z", scale=4)
 
+``scale`` is required for faceted quiver plots. The scale determines the number of data units per arrow length unit, i.e. a smaller scale parameter makes the arrow longer.
 
 .. _plot-maps:
 

From b9bcadaa41bec701666debdfda6b5aac9930d41b Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Fri, 12 Feb 2021 07:05:15 -0700
Subject: [PATCH 25/25] review comments.

---
 xarray/plot/utils.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xarray/plot/utils.py b/xarray/plot/utils.py
index 534a00bbd10..5510cf7f219 100644
--- a/xarray/plot/utils.py
+++ b/xarray/plot/utils.py
@@ -847,6 +847,6 @@ def _get_nice_quiver_magnitude(u, v):
     import matplotlib as mpl
 
     ticker = mpl.ticker.MaxNLocator(3)
-    median = np.mean(np.hypot(u.values, v.values))
-    magnitude = ticker.tick_values(0, median)[-2]
+    mean = np.mean(np.hypot(u.values, v.values))
+    magnitude = ticker.tick_values(0, mean)[-2]
     return magnitude