Deprecating Series.argmin and Series.argmax (pandas-dev#16830)

Author: Lucas Kushner

doc/source/whatsnew/v0.21.0.txt

@@ -116,6 +116,8 @@ Other API Changes
 Deprecations
 ~~~~~~~~~~~~
 - :func:`read_excel()` has deprecated ``sheetname`` in favor of ``sheet_name`` for consistency with ``.to_excel()`` (:issue:`10559`).
+- :func:`Series.argmax` has been deprecated in favor of :func:`Series.idxmax` (:issue:`16830`)
+- :func:`Series.argmin` has been deprecated in favor of :func:`Series.idxmin` (:issue:`16830`)
 
 
 .. _whatsnew_0210.prior_deprecations:

pandas/core/series.py

@@ -71,7 +71,8 @@
 import pandas.core.common as com
 import pandas.core.nanops as nanops
 import pandas.io.formats.format as fmt
-from pandas.util._decorators import Appender, deprecate_kwarg, Substitution
+from pandas.util._decorators import (
+    Appender, deprecate, deprecate_kwarg, Substitution)
 from pandas.util._validators import validate_bool_kwarg
 
 from pandas._libs import index as libindex, tslib as libts, lib, iNaT
@@ -1293,8 +1294,8 @@ def idxmax(self, axis=None, skipna=True, *args, **kwargs):
         return self.index[i]
 
     # ndarray compat
-    argmin = idxmin
-    argmax = idxmax
+    argmin = deprecate('argmin', idxmin)
+    argmax = deprecate('argmax', idxmax)
 
     def round(self, decimals=0, *args, **kwargs):
         """

pandas/tests/series/test_analytics.py

@@ -1210,11 +1210,19 @@ def test_idxmin(self):
         result = s.idxmin()
         assert result == 1
 
-    def test_numpy_argmin(self):
-        # argmin is aliased to idxmin
+    def test_numpy_argmin_deprecated(self):
         data = np.random.randint(0, 11, size=10)
-        result = np.argmin(Series(data))
-        assert result == np.argmin(data)
+
+        with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+            # The deprecation of Series.argmin also causes a deprecation warning
+            # when calling np.argmin
+            result = np.argmin(Series(data))
+            assert result == np.argmin(data)
+
+        with tm.assert_produces_warning(FutureWarning):
+            # argmin is aliased to idxmin
+            result = Series(data).argmin()
+            assert result == Series(data).idxmin()
 
         if not _np_version_under1p10:
             msg = "the 'out' parameter is not supported"
@@ -1265,12 +1273,19 @@ def test_idxmax(self):
         result = s.idxmin()
         assert result == 1.1
 
-    def test_numpy_argmax(self):
-
-        # argmax is aliased to idxmax
+    def test_numpy_argmax_deprecated(self):
         data = np.random.randint(0, 11, size=10)
-        result = np.argmax(Series(data))
-        assert result == np.argmax(data)
+
+        with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+            # The deprecation of Series.argmax also causes a deprecation warning
+            # when calling np.argmax
+            result = np.argmax(Series(data))
+            assert result == np.argmax(data)
+
+        with tm.assert_produces_warning(FutureWarning):
+            # argmax is aliased to idxmax
+            result = Series(data).argmax()
+            assert result == Series(data).idxmax()
 
         if not _np_version_under1p10:
             msg = "the 'out' parameter is not supported"