BUG: Fixed first last valid index (#20499)

Removed old methods from Series and DF
Added new methods into NDFrame
Created new convenient method _find_first_valid

Author: asdf8601

pandas/core/frame.py

@@ -5015,31 +5015,6 @@ def update(self, other, join='left', overwrite=True, filter_func=None,
 
             self[col] = expressions.where(mask, this, that)
 
-    # ----------------------------------------------------------------------
-    # Misc methods
-
-    def _get_valid_indices(self):
-        is_valid = self.count(1) > 0
-        return self.index[is_valid]
-
-    @Appender(_shared_docs['valid_index'] % {
-        'position': 'first', 'klass': 'DataFrame'})
-    def first_valid_index(self):
-        if len(self) == 0:
-            return None
-
-        valid_indices = self._get_valid_indices()
-        return valid_indices[0] if len(valid_indices) else None
-
-    @Appender(_shared_docs['valid_index'] % {
-        'position': 'last', 'klass': 'DataFrame'})
-    def last_valid_index(self):
-        if len(self) == 0:
-            return None
-
-        valid_indices = self._get_valid_indices()
-        return valid_indices[-1] if len(valid_indices) else None
-
     # ----------------------------------------------------------------------
     # Data reshaping
 

pandas/core/generic.py

@@ -8763,6 +8763,37 @@ def transform(self, func, *args, **kwargs):
         scalar : type of index
         """
 
+    def _find_first_valid(self, direction=1):
+        if len(self) == 0:  # early stop
+            return None
+        is_valid = ~self.isna()
+
+        if self.ndim == 2:
+            is_valid = is_valid.any(1)  # reduce axis 1
+
+        if direction == 1:
+            i = is_valid.idxmax()
+            if not is_valid[i]:
+                return None
+            else:
+                return i
+        elif direction == -1:
+            i = is_valid.values[::-1].argmax()
+            if not is_valid.iat[len(self) - i - 1]:
+                return None
+            else:
+                return self.index[len(self) - i - 1]
+
+    @Appender(_shared_docs['valid_index'] % {'position': 'first',
+                                             'klass': 'NDFrame'})
+    def first_valid_index(self):
+        return self._find_first_valid(1)
+
+    @Appender(_shared_docs['valid_index'] % {'position': 'last',
+                                             'klass': 'NDFrame'})
+    def last_valid_index(self):
+        return self._find_first_valid(-1)
+
 
 def _doc_parms(cls):
     """Return a tuple of the doc parms."""

pandas/core/series.py

@@ -3887,32 +3887,6 @@ def valid(self, inplace=False, **kwargs):
                       "Use .dropna instead.", FutureWarning, stacklevel=2)
         return self.dropna(inplace=inplace, **kwargs)
 
-    @Appender(generic._shared_docs['valid_index'] % {
-        'position': 'first', 'klass': 'Series'})
-    def first_valid_index(self):
-        if len(self) == 0:
-            return None
-
-        mask = isna(self._values)
-        i = mask.argmin()
-        if mask[i]:
-            return None
-        else:
-            return self.index[i]
-
-    @Appender(generic._shared_docs['valid_index'] % {
-        'position': 'last', 'klass': 'Series'})
-    def last_valid_index(self):
-        if len(self) == 0:
-            return None
-
-        mask = isna(self._values[::-1])
-        i = mask.argmin()
-        if mask[i]:
-            return None
-        else:
-            return self.index[len(self) - i - 1]
-
     # ----------------------------------------------------------------------
     # Time series-oriented methods