From 6151181c2cc0a2019d17f74cf85a09802bc39c4a Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Fri, 15 Jun 2018 17:42:16 +0530
Subject: [PATCH 01/20] Initial commit

GH21441
---
 doc/source/whatsnew/v0.23.2.txt      |  6 +++++-
 pandas/core/generic.py               | 14 +++++++-------
 pandas/tests/generic/test_generic.py | 10 ++++++++++
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/doc/source/whatsnew/v0.23.2.txt b/doc/source/whatsnew/v0.23.2.txt
index 79a4c3da2ffa4..1edeb3662fc82 100644
--- a/doc/source/whatsnew/v0.23.2.txt
+++ b/doc/source/whatsnew/v0.23.2.txt
@@ -16,8 +16,12 @@ and bug fixes. We recommend that all users upgrade to this version.
 Fixed Regressions
 ~~~~~~~~~~~~~~~~~
 
+- 
 -
--
+
+**Other Fixes**
+
+- Bug in :meth:`first_valid_index` that raised for row index with duplicate values (:issue:`21441`)
 
 .. _whatsnew_0232.performance:
 
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 32f64b1d3e05c..a060e5b2850c9 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8970,17 +8970,17 @@ def _find_valid_index(self, how):
 
         if how == 'first':
             # First valid value case
-            i = is_valid.idxmax()
-            if not is_valid[i]:
-                return None
-            return i
+            i = is_valid.values[::].argmin()
+            idxpos = i
 
         elif how == 'last':
             # Last valid value case
             i = is_valid.values[::-1].argmax()
-            if not is_valid.iat[len(self) - i - 1]:
-                return None
-            return self.index[len(self) - i - 1]
+            idxpos = len(self) - i - 1
+
+        if not is_valid.iat[idxpos]:
+            return None
+        return self.index[idxpos]
 
     @Appender(_shared_docs['valid_index'] % {'position': 'first',
                                              'klass': 'NDFrame'})
diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 311c71f734945..618b2e8206baf 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -612,6 +612,16 @@ def test_pct_change(self, periods, fill_method, limit, exp):
         else:
             tm.assert_series_equal(res, Series(exp))
 
+    @pytest.mark.parametrize("DF,idx,first_idx,last_idx", [
+        ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
+        ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
+        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd')])
+    def test_valid_index(self, DF, idx, first_idx, last_idx):
+        # GH 21441
+        df1 = pd.DataFrame(DF, index=idx)
+        assert first_idx == df1.first_valid_index()
+        assert last_idx == df1.last_valid_index()
+
 
 class TestNDFrame(object):
     # tests that don't fit elsewhere

From 003f801bb23e4ce6840817893aa4843c2245e456 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sat, 16 Jun 2018 11:32:58 +0530
Subject: [PATCH 02/20] Removed failing test from closed PR

GH21441
---
 doc/source/whatsnew/v0.23.2.txt      |  6 +-----
 pandas/core/generic.py               |  7 ++-----
 pandas/tests/generic/test_generic.py | 10 +++++-----
 pandas/tests/test_resample.py        |  7 -------
 4 files changed, 8 insertions(+), 22 deletions(-)

diff --git a/doc/source/whatsnew/v0.23.2.txt b/doc/source/whatsnew/v0.23.2.txt
index 1edeb3662fc82..0646c8c2d6d17 100644
--- a/doc/source/whatsnew/v0.23.2.txt
+++ b/doc/source/whatsnew/v0.23.2.txt
@@ -16,13 +16,9 @@ and bug fixes. We recommend that all users upgrade to this version.
 Fixed Regressions
 ~~~~~~~~~~~~~~~~~
 
-- 
+- Bug in :meth:`first_valid_index` raised for a row index with duplicate values (:issue:`21441`)
 -
 
-**Other Fixes**
-
-- Bug in :meth:`first_valid_index` that raised for row index with duplicate values (:issue:`21441`)
-
 .. _whatsnew_0232.performance:
 
 Performance Improvements
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index a060e5b2850c9..9356461951899 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8970,13 +8970,10 @@ def _find_valid_index(self, how):
 
         if how == 'first':
             # First valid value case
-            i = is_valid.values[::].argmin()
-            idxpos = i
-
+            idxpos = is_valid.values[::].argmin()
         elif how == 'last':
             # Last valid value case
-            i = is_valid.values[::-1].argmax()
-            idxpos = len(self) - i - 1
+            idxpos = len(self) - 1 - is_valid.values[::-1].argmax()
 
         if not is_valid.iat[idxpos]:
             return None
diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 618b2e8206baf..9e28fd7af8a8c 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -612,15 +612,15 @@ def test_pct_change(self, periods, fill_method, limit, exp):
         else:
             tm.assert_series_equal(res, Series(exp))
 
-    @pytest.mark.parametrize("DF,idx,first_idx,last_idx", [
+    @pytest.mark.parametrize("data,index,expected_first,expected_last", [
         ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
         ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
         ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd')])
-    def test_valid_index(self, DF, idx, first_idx, last_idx):
+    def test_valid_index(self, data, index, expected_first, expected_last):
         # GH 21441
-        df1 = pd.DataFrame(DF, index=idx)
-        assert first_idx == df1.first_valid_index()
-        assert last_idx == df1.last_valid_index()
+        df = DataFrame(data, index=index)
+        assert expected_first == df.first_valid_index()
+        assert expected_last == df.last_valid_index()
 
 
 class TestNDFrame(object):
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index c1257cce9a9a4..00610db795954 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -649,13 +649,6 @@ def test_asfreq_fill_value(self):
         expected = frame.reindex(new_index, fill_value=4.0)
         assert_frame_equal(result, expected)
 
-    def test_resample_interpolate(self):
-        # # 12925
-        df = self.create_series().to_frame('value')
-        assert_frame_equal(
-            df.resample('1T').asfreq().interpolate(),
-            df.resample('1T').interpolate())
-
     def test_raises_on_non_datetimelike_index(self):
         # this is a non datetimelike index
         xp = DataFrame()

From 952758ab726f2f738bc54d1bf5011f083493ceed Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sun, 17 Jun 2018 21:21:15 +0530
Subject: [PATCH 03/20] Updated logic

GH21441
---
 pandas/core/generic.py | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 9356461951899..b00a1b15e8303 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8968,16 +8968,20 @@ def _find_valid_index(self, how):
         if self.ndim == 2:
             is_valid = is_valid.any(1)  # reduce axis 1
 
-        if how == 'first':
-            # First valid value case
-            idxpos = is_valid.values[::].argmin()
-        elif how == 'last':
-            # Last valid value case
-            idxpos = len(self) - 1 - is_valid.values[::-1].argmax()
-
-        if not is_valid.iat[idxpos]:
+        if how == 'last':
+            is_valid.sort_index(ascending=False, inplace=True)
+
+        idxpos = is_valid.idxmax()
+
+        if isinstance(is_valid[idxpos], ABCSeries):
+            for chk_notna in is_valid[idxpos]:
+                chk_notna = True and chk_notna
+        else:
+            chk_notna = is_valid[idxpos]
+
+        if not chk_notna:
             return None
-        return self.index[idxpos]
+        return idxpos
 
     @Appender(_shared_docs['valid_index'] % {'position': 'first',
                                              'klass': 'NDFrame'})

From 1f4beb0c109fea466969d89caad544f097b18f7b Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sun, 17 Jun 2018 21:37:55 +0530
Subject: [PATCH 04/20] Changed logic from AND to OR for chk_notna

GH21441
---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index b00a1b15e8303..db8a5577c2cfb 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8975,7 +8975,7 @@ def _find_valid_index(self, how):
 
         if isinstance(is_valid[idxpos], ABCSeries):
             for chk_notna in is_valid[idxpos]:
-                chk_notna = True and chk_notna
+                chk_notna = False or chk_notna
         else:
             chk_notna = is_valid[idxpos]
 

From 675201d9a0c14e81f206cb35f78fc10230e5dc39 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sun, 17 Jun 2018 22:37:11 +0530
Subject: [PATCH 05/20] Series reverse logic for how == last, edits to whatsnew

GH21441
---
 doc/source/whatsnew/v0.23.2.txt | 2 +-
 pandas/core/generic.py          | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/source/whatsnew/v0.23.2.txt b/doc/source/whatsnew/v0.23.2.txt
index 0646c8c2d6d17..1c7b64befdbb7 100644
--- a/doc/source/whatsnew/v0.23.2.txt
+++ b/doc/source/whatsnew/v0.23.2.txt
@@ -16,7 +16,7 @@ and bug fixes. We recommend that all users upgrade to this version.
 Fixed Regressions
 ~~~~~~~~~~~~~~~~~
 
-- Bug in :meth:`first_valid_index` raised for a row index with duplicate values (:issue:`21441`)
+- Bug in both :meth:`DataFrame.first_valid_index` and :meth:`Series.first_valid_index` raised for a row index with duplicate values (:issue:`21441`)
 -
 
 .. _whatsnew_0232.performance:
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index db8a5577c2cfb..8fbc03a9563ae 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8969,7 +8969,7 @@ def _find_valid_index(self, how):
             is_valid = is_valid.any(1)  # reduce axis 1
 
         if how == 'last':
-            is_valid.sort_index(ascending=False, inplace=True)
+            is_valid = is_valid[::-1]
 
         idxpos = is_valid.idxmax()
 

From 06402799673ba432b6f5219bfc89b4b67801eaa8 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Mon, 18 Jun 2018 07:37:24 +0530
Subject: [PATCH 06/20] Reverting how==last logic to original, restoring
 deleted test

GH21441
---
 pandas/core/generic.py        | 22 ++++++++++++----------
 pandas/tests/test_resample.py |  7 +++++++
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 8fbc03a9563ae..3ff1b1da1fdfb 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8968,20 +8968,22 @@ def _find_valid_index(self, how):
         if self.ndim == 2:
             is_valid = is_valid.any(1)  # reduce axis 1
 
-        if how == 'last':
-            is_valid = is_valid[::-1]
-
-        idxpos = is_valid.idxmax()
+        if how == 'first':
+            idx = is_valid.idxmax()
+            if isinstance(is_valid[idx], ABCSeries):
+                for chk_notna in is_valid[idx]:
+                    chk_notna = False or chk_notna
+            else:
+                chk_notna = is_valid[idx]
 
-        if isinstance(is_valid[idxpos], ABCSeries):
-            for chk_notna in is_valid[idxpos]:
-                chk_notna = False or chk_notna
-        else:
-            chk_notna = is_valid[idxpos]
+        if how == 'last':
+            idxpos = len(self) - 1 - is_valid.values[::-1].argmax()
+            chk_notna = is_valid.iat[idxpos]
+            idx = self.index[idxpos]
 
         if not chk_notna:
             return None
-        return idxpos
+        return idx
 
     @Appender(_shared_docs['valid_index'] % {'position': 'first',
                                              'klass': 'NDFrame'})
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 00610db795954..c1257cce9a9a4 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -649,6 +649,13 @@ def test_asfreq_fill_value(self):
         expected = frame.reindex(new_index, fill_value=4.0)
         assert_frame_equal(result, expected)
 
+    def test_resample_interpolate(self):
+        # # 12925
+        df = self.create_series().to_frame('value')
+        assert_frame_equal(
+            df.resample('1T').asfreq().interpolate(),
+            df.resample('1T').interpolate())
+
     def test_raises_on_non_datetimelike_index(self):
         # this is a non datetimelike index
         xp = DataFrame()

From 177a3f4e830a730a0a332c88d6239c042f86e891 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Tue, 19 Jun 2018 07:56:26 +0530
Subject: [PATCH 07/20] Fixed the if / for for chk_notna, added test cases for
 NA values in duplicate index

GH21441
---
 pandas/core/generic.py               | 5 +++--
 pandas/tests/generic/test_generic.py | 5 ++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 3ff1b1da1fdfb..d572cf5e955ca 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8971,8 +8971,9 @@ def _find_valid_index(self, how):
         if how == 'first':
             idx = is_valid.idxmax()
             if isinstance(is_valid[idx], ABCSeries):
-                for chk_notna in is_valid[idx]:
-                    chk_notna = False or chk_notna
+                chk_notna = False
+                for idxinstance in is_valid[idx]:
+                    chk_notna = chk_notna or idxinstance
             else:
                 chk_notna = is_valid[idx]
 
diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 9e28fd7af8a8c..20472e06e2153 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -615,7 +615,10 @@ def test_pct_change(self, periods, fill_method, limit, exp):
     @pytest.mark.parametrize("data,index,expected_first,expected_last", [
         ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
         ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
-        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd')])
+        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd'),
+        ({'A': [1, np.nan, 3]}, [1, 1, 2], 1, 2),
+        ({'A': [np.nan, np.nan, 3]}, [1, 1, 2], 2, 2),
+        ({'A': [1, np.nan, 3]}, [1, 2, 2], 1, 2)])
     def test_valid_index(self, data, index, expected_first, expected_last):
         # GH 21441
         df = DataFrame(data, index=index)

From e94aad5e170ae9e06a5a41297875826db88b3775 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Fri, 15 Jun 2018 17:42:16 +0530
Subject: [PATCH 08/20] Initial commit

GH21441
---
 doc/source/whatsnew/v0.23.2.txt      |  3 ++-
 pandas/core/generic.py               | 14 +++++++-------
 pandas/tests/generic/test_generic.py | 10 ++++++++++
 3 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/doc/source/whatsnew/v0.23.2.txt b/doc/source/whatsnew/v0.23.2.txt
index 0f2c9c4756987..154f998b01c1a 100644
--- a/doc/source/whatsnew/v0.23.2.txt
+++ b/doc/source/whatsnew/v0.23.2.txt
@@ -16,8 +16,9 @@ and bug fixes. We recommend that all users upgrade to this version.
 Fixed Regressions
 ~~~~~~~~~~~~~~~~~
 
+
 - Fixed regression in :meth:`to_csv` when handling file-like object incorrectly (:issue:`21471`)
--
+- 
 
 .. _whatsnew_0232.performance:
 
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 32f64b1d3e05c..a060e5b2850c9 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8970,17 +8970,17 @@ def _find_valid_index(self, how):
 
         if how == 'first':
             # First valid value case
-            i = is_valid.idxmax()
-            if not is_valid[i]:
-                return None
-            return i
+            i = is_valid.values[::].argmin()
+            idxpos = i
 
         elif how == 'last':
             # Last valid value case
             i = is_valid.values[::-1].argmax()
-            if not is_valid.iat[len(self) - i - 1]:
-                return None
-            return self.index[len(self) - i - 1]
+            idxpos = len(self) - i - 1
+
+        if not is_valid.iat[idxpos]:
+            return None
+        return self.index[idxpos]
 
     @Appender(_shared_docs['valid_index'] % {'position': 'first',
                                              'klass': 'NDFrame'})
diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 311c71f734945..618b2e8206baf 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -612,6 +612,16 @@ def test_pct_change(self, periods, fill_method, limit, exp):
         else:
             tm.assert_series_equal(res, Series(exp))
 
+    @pytest.mark.parametrize("DF,idx,first_idx,last_idx", [
+        ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
+        ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
+        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd')])
+    def test_valid_index(self, DF, idx, first_idx, last_idx):
+        # GH 21441
+        df1 = pd.DataFrame(DF, index=idx)
+        assert first_idx == df1.first_valid_index()
+        assert last_idx == df1.last_valid_index()
+
 
 class TestNDFrame(object):
     # tests that don't fit elsewhere

From ff58ffd0e77832e298fbda7183ca0666dba7e81b Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sat, 16 Jun 2018 11:32:58 +0530
Subject: [PATCH 09/20] Removed failing test from closed PR

GH21441
---
 doc/source/whatsnew/v0.23.2.txt      |  1 -
 pandas/core/generic.py               |  7 ++-----
 pandas/tests/generic/test_generic.py | 10 +++++-----
 pandas/tests/test_resample.py        |  7 -------
 4 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/doc/source/whatsnew/v0.23.2.txt b/doc/source/whatsnew/v0.23.2.txt
index 154f998b01c1a..7629b86e26bf7 100644
--- a/doc/source/whatsnew/v0.23.2.txt
+++ b/doc/source/whatsnew/v0.23.2.txt
@@ -16,7 +16,6 @@ and bug fixes. We recommend that all users upgrade to this version.
 Fixed Regressions
 ~~~~~~~~~~~~~~~~~
 
-
 - Fixed regression in :meth:`to_csv` when handling file-like object incorrectly (:issue:`21471`)
 - 
 
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index a060e5b2850c9..9356461951899 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8970,13 +8970,10 @@ def _find_valid_index(self, how):
 
         if how == 'first':
             # First valid value case
-            i = is_valid.values[::].argmin()
-            idxpos = i
-
+            idxpos = is_valid.values[::].argmin()
         elif how == 'last':
             # Last valid value case
-            i = is_valid.values[::-1].argmax()
-            idxpos = len(self) - i - 1
+            idxpos = len(self) - 1 - is_valid.values[::-1].argmax()
 
         if not is_valid.iat[idxpos]:
             return None
diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 618b2e8206baf..9e28fd7af8a8c 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -612,15 +612,15 @@ def test_pct_change(self, periods, fill_method, limit, exp):
         else:
             tm.assert_series_equal(res, Series(exp))
 
-    @pytest.mark.parametrize("DF,idx,first_idx,last_idx", [
+    @pytest.mark.parametrize("data,index,expected_first,expected_last", [
         ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
         ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
         ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd')])
-    def test_valid_index(self, DF, idx, first_idx, last_idx):
+    def test_valid_index(self, data, index, expected_first, expected_last):
         # GH 21441
-        df1 = pd.DataFrame(DF, index=idx)
-        assert first_idx == df1.first_valid_index()
-        assert last_idx == df1.last_valid_index()
+        df = DataFrame(data, index=index)
+        assert expected_first == df.first_valid_index()
+        assert expected_last == df.last_valid_index()
 
 
 class TestNDFrame(object):
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 6f0ad0535c6b4..42c7051437044 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -649,13 +649,6 @@ def test_asfreq_fill_value(self):
         expected = frame.reindex(new_index, fill_value=4.0)
         assert_frame_equal(result, expected)
 
-    def test_resample_interpolate(self):
-        # # 12925
-        df = self.create_series().to_frame('value')
-        assert_frame_equal(
-            df.resample('1T').asfreq().interpolate(),
-            df.resample('1T').interpolate())
-
     def test_raises_on_non_datetimelike_index(self):
         # this is a non datetimelike index
         xp = DataFrame()

From d326b0a778359be2d297f6c52ef6caad66b949cc Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sun, 17 Jun 2018 21:21:15 +0530
Subject: [PATCH 10/20] Updated logic

GH21441
---
 pandas/core/generic.py | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 9356461951899..b00a1b15e8303 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8968,16 +8968,20 @@ def _find_valid_index(self, how):
         if self.ndim == 2:
             is_valid = is_valid.any(1)  # reduce axis 1
 
-        if how == 'first':
-            # First valid value case
-            idxpos = is_valid.values[::].argmin()
-        elif how == 'last':
-            # Last valid value case
-            idxpos = len(self) - 1 - is_valid.values[::-1].argmax()
-
-        if not is_valid.iat[idxpos]:
+        if how == 'last':
+            is_valid.sort_index(ascending=False, inplace=True)
+
+        idxpos = is_valid.idxmax()
+
+        if isinstance(is_valid[idxpos], ABCSeries):
+            for chk_notna in is_valid[idxpos]:
+                chk_notna = True and chk_notna
+        else:
+            chk_notna = is_valid[idxpos]
+
+        if not chk_notna:
             return None
-        return self.index[idxpos]
+        return idxpos
 
     @Appender(_shared_docs['valid_index'] % {'position': 'first',
                                              'klass': 'NDFrame'})

From b53bb117550bddb1c95911eedd5086a1bf9669bd Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sun, 17 Jun 2018 21:37:55 +0530
Subject: [PATCH 11/20] Changed logic from AND to OR for chk_notna

GH21441
---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index b00a1b15e8303..db8a5577c2cfb 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8975,7 +8975,7 @@ def _find_valid_index(self, how):
 
         if isinstance(is_valid[idxpos], ABCSeries):
             for chk_notna in is_valid[idxpos]:
-                chk_notna = True and chk_notna
+                chk_notna = False or chk_notna
         else:
             chk_notna = is_valid[idxpos]
 

From 0cb340577ba22a64555d75f25fab635deedb6505 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Sun, 17 Jun 2018 22:37:11 +0530
Subject: [PATCH 12/20] Series reverse logic for how == last, edits to whatsnew

GH21441
---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index db8a5577c2cfb..8fbc03a9563ae 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8969,7 +8969,7 @@ def _find_valid_index(self, how):
             is_valid = is_valid.any(1)  # reduce axis 1
 
         if how == 'last':
-            is_valid.sort_index(ascending=False, inplace=True)
+            is_valid = is_valid[::-1]
 
         idxpos = is_valid.idxmax()
 

From 11edb51892c2fd106537841bc1fa881c88fe2322 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Mon, 18 Jun 2018 07:37:24 +0530
Subject: [PATCH 13/20] Reverting how==last logic to original, restoring
 deleted test

GH21441
---
 pandas/core/generic.py        | 22 ++++++++++++----------
 pandas/tests/test_resample.py |  7 +++++++
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 8fbc03a9563ae..3ff1b1da1fdfb 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8968,20 +8968,22 @@ def _find_valid_index(self, how):
         if self.ndim == 2:
             is_valid = is_valid.any(1)  # reduce axis 1
 
-        if how == 'last':
-            is_valid = is_valid[::-1]
-
-        idxpos = is_valid.idxmax()
+        if how == 'first':
+            idx = is_valid.idxmax()
+            if isinstance(is_valid[idx], ABCSeries):
+                for chk_notna in is_valid[idx]:
+                    chk_notna = False or chk_notna
+            else:
+                chk_notna = is_valid[idx]
 
-        if isinstance(is_valid[idxpos], ABCSeries):
-            for chk_notna in is_valid[idxpos]:
-                chk_notna = False or chk_notna
-        else:
-            chk_notna = is_valid[idxpos]
+        if how == 'last':
+            idxpos = len(self) - 1 - is_valid.values[::-1].argmax()
+            chk_notna = is_valid.iat[idxpos]
+            idx = self.index[idxpos]
 
         if not chk_notna:
             return None
-        return idxpos
+        return idx
 
     @Appender(_shared_docs['valid_index'] % {'position': 'first',
                                              'klass': 'NDFrame'})
diff --git a/pandas/tests/test_resample.py b/pandas/tests/test_resample.py
index 42c7051437044..6f0ad0535c6b4 100644
--- a/pandas/tests/test_resample.py
+++ b/pandas/tests/test_resample.py
@@ -649,6 +649,13 @@ def test_asfreq_fill_value(self):
         expected = frame.reindex(new_index, fill_value=4.0)
         assert_frame_equal(result, expected)
 
+    def test_resample_interpolate(self):
+        # # 12925
+        df = self.create_series().to_frame('value')
+        assert_frame_equal(
+            df.resample('1T').asfreq().interpolate(),
+            df.resample('1T').interpolate())
+
     def test_raises_on_non_datetimelike_index(self):
         # this is a non datetimelike index
         xp = DataFrame()

From ed410e1565da8964e79adffbcbb9bb5a275b0c4e Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Tue, 19 Jun 2018 07:56:26 +0530
Subject: [PATCH 14/20] Fixed the if / for for chk_notna, added test cases for
 NA values in duplicate index

GH21441
---
 pandas/core/generic.py               | 5 +++--
 pandas/tests/generic/test_generic.py | 5 ++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 3ff1b1da1fdfb..d572cf5e955ca 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8971,8 +8971,9 @@ def _find_valid_index(self, how):
         if how == 'first':
             idx = is_valid.idxmax()
             if isinstance(is_valid[idx], ABCSeries):
-                for chk_notna in is_valid[idx]:
-                    chk_notna = False or chk_notna
+                chk_notna = False
+                for idxinstance in is_valid[idx]:
+                    chk_notna = chk_notna or idxinstance
             else:
                 chk_notna = is_valid[idx]
 
diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 9e28fd7af8a8c..20472e06e2153 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -615,7 +615,10 @@ def test_pct_change(self, periods, fill_method, limit, exp):
     @pytest.mark.parametrize("data,index,expected_first,expected_last", [
         ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
         ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
-        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd')])
+        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd'),
+        ({'A': [1, np.nan, 3]}, [1, 1, 2], 1, 2),
+        ({'A': [np.nan, np.nan, 3]}, [1, 1, 2], 2, 2),
+        ({'A': [1, np.nan, 3]}, [1, 2, 2], 1, 2)])
     def test_valid_index(self, data, index, expected_first, expected_last):
         # GH 21441
         df = DataFrame(data, index=index)

From 05e8a9968d1acb8a5f9ee13400e3ec8894c72702 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Tue, 19 Jun 2018 08:06:36 +0530
Subject: [PATCH 15/20] Rebased and updated whatsnew

GH21441
---
 doc/source/whatsnew/v0.23.2.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v0.23.2.txt b/doc/source/whatsnew/v0.23.2.txt
index 7629b86e26bf7..09bf337bf0938 100644
--- a/doc/source/whatsnew/v0.23.2.txt
+++ b/doc/source/whatsnew/v0.23.2.txt
@@ -17,6 +17,7 @@ Fixed Regressions
 ~~~~~~~~~~~~~~~~~
 
 - Fixed regression in :meth:`to_csv` when handling file-like object incorrectly (:issue:`21471`)
+- Bug in both :meth:`DataFrame.first_valid_index` and :meth:`Series.first_valid_index` raised for a row index with duplicate values (:issue:`21441`)
 - 
 
 .. _whatsnew_0232.performance:

From 01a9f7ee8b07efdc314c76b1579fe652d3ba5b5c Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Tue, 19 Jun 2018 19:01:21 +0530
Subject: [PATCH 16/20] Moved tests to test_timeseries

GH21441
---
 pandas/tests/frame/test_timeseries.py | 15 ++++++++++++++-
 pandas/tests/generic/test_generic.py  | 13 -------------
 2 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/pandas/tests/frame/test_timeseries.py b/pandas/tests/frame/test_timeseries.py
index 90fbc6e628369..4c9c2a8ae1557 100644
--- a/pandas/tests/frame/test_timeseries.py
+++ b/pandas/tests/frame/test_timeseries.py
@@ -506,7 +506,15 @@ def test_asfreq_fillvalue(self):
         actual_series = ts.asfreq(freq='1S', fill_value=9.0)
         assert_series_equal(expected_series, actual_series)
 
-    def test_first_last_valid(self):
+    @pytest.mark.parametrize("data,index,expected_first,expected_last", [
+        ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
+        ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
+        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd'),
+        ({'A': [1, np.nan, 3]}, [1, 1, 2], 1, 2),
+        ({'A': [np.nan, np.nan, 3]}, [1, 1, 2], 2, 2),
+        ({'A': [1, np.nan, 3]}, [1, 2, 2], 1, 2)])
+    def test_first_last_valid(self, data, index,
+                              expected_first, expected_last):
         N = len(self.frame.index)
         mat = randn(N)
         mat[:5] = nan
@@ -539,6 +547,11 @@ def test_first_last_valid(self):
         assert frame.first_valid_index().freq == frame.index.freq
         assert frame.last_valid_index().freq == frame.index.freq
 
+        # GH 21441
+        df = DataFrame(data, index=index)
+        assert expected_first == df.first_valid_index()
+        assert expected_last == df.last_valid_index()
+
     def test_first_subset(self):
         ts = tm.makeTimeDataFrame(freq='12h')
         result = ts.first('10d')
diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 20472e06e2153..311c71f734945 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -612,19 +612,6 @@ def test_pct_change(self, periods, fill_method, limit, exp):
         else:
             tm.assert_series_equal(res, Series(exp))
 
-    @pytest.mark.parametrize("data,index,expected_first,expected_last", [
-        ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
-        ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
-        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd'),
-        ({'A': [1, np.nan, 3]}, [1, 1, 2], 1, 2),
-        ({'A': [np.nan, np.nan, 3]}, [1, 1, 2], 2, 2),
-        ({'A': [1, np.nan, 3]}, [1, 2, 2], 1, 2)])
-    def test_valid_index(self, data, index, expected_first, expected_last):
-        # GH 21441
-        df = DataFrame(data, index=index)
-        assert expected_first == df.first_valid_index()
-        assert expected_last == df.last_valid_index()
-
 
 class TestNDFrame(object):
     # tests that don't fit elsewhere

From 111efb01d97446bc5f72a2ed4d5f26ac3e0ea314 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Tue, 19 Jun 2018 19:16:42 +0530
Subject: [PATCH 17/20] Removed tests from test_generic

GH21441
---
 pandas/tests/generic/test_generic.py | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/pandas/tests/generic/test_generic.py b/pandas/tests/generic/test_generic.py
index 20472e06e2153..311c71f734945 100644
--- a/pandas/tests/generic/test_generic.py
+++ b/pandas/tests/generic/test_generic.py
@@ -612,19 +612,6 @@ def test_pct_change(self, periods, fill_method, limit, exp):
         else:
             tm.assert_series_equal(res, Series(exp))
 
-    @pytest.mark.parametrize("data,index,expected_first,expected_last", [
-        ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
-        ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
-        ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd'),
-        ({'A': [1, np.nan, 3]}, [1, 1, 2], 1, 2),
-        ({'A': [np.nan, np.nan, 3]}, [1, 1, 2], 2, 2),
-        ({'A': [1, np.nan, 3]}, [1, 2, 2], 1, 2)])
-    def test_valid_index(self, data, index, expected_first, expected_last):
-        # GH 21441
-        df = DataFrame(data, index=index)
-        assert expected_first == df.first_valid_index()
-        assert expected_last == df.last_valid_index()
-
 
 class TestNDFrame(object):
     # tests that don't fit elsewhere

From 608c09e3346d758c19912b3ede9330dbfd2c5d7a Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Tue, 19 Jun 2018 20:50:57 +0530
Subject: [PATCH 18/20] Updated test parameter name

GH21441
---
 pandas/tests/frame/test_timeseries.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/tests/frame/test_timeseries.py b/pandas/tests/frame/test_timeseries.py
index 4c9c2a8ae1557..fb9bd74d9876d 100644
--- a/pandas/tests/frame/test_timeseries.py
+++ b/pandas/tests/frame/test_timeseries.py
@@ -506,14 +506,14 @@ def test_asfreq_fillvalue(self):
         actual_series = ts.asfreq(freq='1S', fill_value=9.0)
         assert_series_equal(expected_series, actual_series)
 
-    @pytest.mark.parametrize("data,index,expected_first,expected_last", [
+    @pytest.mark.parametrize("data,idx,expected_first,expected_last", [
         ({'A': [1, 2, 3]}, [1, 1, 2], 1, 2),
         ({'A': [1, 2, 3]}, [1, 2, 2], 1, 2),
         ({'A': [1, 2, 3, 4]}, ['d', 'd', 'd', 'd'], 'd', 'd'),
         ({'A': [1, np.nan, 3]}, [1, 1, 2], 1, 2),
         ({'A': [np.nan, np.nan, 3]}, [1, 1, 2], 2, 2),
         ({'A': [1, np.nan, 3]}, [1, 2, 2], 1, 2)])
-    def test_first_last_valid(self, data, index,
+    def test_first_last_valid(self, data, idx,
                               expected_first, expected_last):
         N = len(self.frame.index)
         mat = randn(N)
@@ -548,7 +548,7 @@ def test_first_last_valid(self, data, index,
         assert frame.last_valid_index().freq == frame.index.freq
 
         # GH 21441
-        df = DataFrame(data, index=index)
+        df = DataFrame(data, index=idx)
         assert expected_first == df.first_valid_index()
         assert expected_last == df.last_valid_index()
 

From d8fface58e37dd1baad1fd3daea56e7420f185e7 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Tue, 19 Jun 2018 22:19:39 +0530
Subject: [PATCH 19/20] Minor update to whatsnew to force TravisCI build

GH21441
---
 doc/source/whatsnew/v0.23.2.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v0.23.2.txt b/doc/source/whatsnew/v0.23.2.txt
index 09bf337bf0938..2112b68c32bae 100644
--- a/doc/source/whatsnew/v0.23.2.txt
+++ b/doc/source/whatsnew/v0.23.2.txt
@@ -17,7 +17,7 @@ Fixed Regressions
 ~~~~~~~~~~~~~~~~~
 
 - Fixed regression in :meth:`to_csv` when handling file-like object incorrectly (:issue:`21471`)
-- Bug in both :meth:`DataFrame.first_valid_index` and :meth:`Series.first_valid_index` raised for a row index with duplicate values (:issue:`21441`)
+- Bug in both :meth:`DataFrame.first_valid_index` and :meth:`Series.first_valid_index` raised for a row index having duplicate values (:issue:`21441`)
 - 
 
 .. _whatsnew_0232.performance:

From 751046d1cfbc3f832394703ef6cc994e2cabc686 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Wed, 20 Jun 2018 07:41:31 +0530
Subject: [PATCH 20/20] Mirrored logic for how == first and last

GH21441
---
 pandas/core/generic.py | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index d572cf5e955ca..c37516d478d84 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8969,18 +8969,13 @@ def _find_valid_index(self, how):
             is_valid = is_valid.any(1)  # reduce axis 1
 
         if how == 'first':
-            idx = is_valid.idxmax()
-            if isinstance(is_valid[idx], ABCSeries):
-                chk_notna = False
-                for idxinstance in is_valid[idx]:
-                    chk_notna = chk_notna or idxinstance
-            else:
-                chk_notna = is_valid[idx]
+            idxpos = is_valid.values[::].argmax()
 
         if how == 'last':
             idxpos = len(self) - 1 - is_valid.values[::-1].argmax()
-            chk_notna = is_valid.iat[idxpos]
-            idx = self.index[idxpos]
+
+        chk_notna = is_valid.iat[idxpos]
+        idx = self.index[idxpos]
 
         if not chk_notna:
             return None