Improve name concat (pydata#2792)

* Added tests of desired name inferring behaviour

* Infers names

* updated what's new

Author: TomNicholas

doc/whats-new.rst

@@ -114,6 +114,11 @@ Bug fixes
 - Fixed error when trying to reduce a DataArray using a function which does not
   require an axis argument. (:issue:`2768`)
   By `Tom Nicholas <http://github.com/TomNicholas>`_.
+- Concatenating a sequence of :py:class:`~xarray.DataArray` with varying names
+  sets the name of the output array to ``None``, instead of the name of the
+  first input array. If the names are the same it sets the name to that,
+  instead to the name of the first DataArray in the list as it did before.
+  (:issue:`2775`). By `Tom Nicholas <http://github.com/TomNicholas>`_.
 
 - Per `CF conventions
   <http://cfconventions.org/cf-conventions/cf-conventions.html#calendar>`_,

xarray/core/combine.py

@@ -9,6 +9,7 @@
 from .merge import merge
 from .variable import IndexVariable, Variable, as_variable
 from .variable import concat as concat_vars
+from .computation import result_name
 
 
 def concat(objs, dim=None, data_vars='all', coords='different',
@@ -336,7 +337,10 @@ def _dataarray_concat(arrays, dim, data_vars, coords, compat,
 
     ds = _dataset_concat(datasets, dim, data_vars, coords, compat,
                          positions)
-    return arrays[0]._from_temp_dataset(ds, name)
+    result = arrays[0]._from_temp_dataset(ds, name)
+
+    result.name = result_name(arrays)
+    return result
 
 
 def _auto_concat(datasets, dim=None, data_vars='all', coords='different'):

xarray/tests/test_combine.py

@@ -285,6 +285,15 @@ def test_concat_encoding(self):
         assert concat([foo, foo], dim="x").encoding == foo.encoding
         assert concat([ds, ds], dim="x").encoding == ds.encoding
 
+    @pytest.mark.parametrize("colors, expected_name",
+                             [(['blue', 'green', 'red'], None),
+                              (['red', 'red', 'red'], 'red')])
+    def test_concat_determine_name(self, colors, expected_name):
+        das = [DataArray(np.random.random((2, 2)), dims=['x', 'y'], name=k)
+               for k in colors]
+        result = concat(das, dim="band")
+        assert result.name is expected_name
+
     @requires_dask
     def test_concat_lazy(self):
         import dask.array as da