FEAT-#1285: Add sem implementation for Series and DataFrame

docs/supported_apis/dataframe_supported.rst

@@ -328,7 +328,7 @@ default to pandas.
 +----------------------------+---------------------------+------------------------+----------------------------------------------------+
 | ``select_dtypes``          | `select_dtypes`_          | Y                      |                                                    |
 +----------------------------+---------------------------+------------------------+----------------------------------------------------+
-| ``sem``                    | `sem`_                    | D                      |                                                    |
+| ``sem``                    | `sem`_                    | Y                      |                                                    |
 +----------------------------+---------------------------+------------------------+----------------------------------------------------+
 | ``set_axis``               | `set_axis`_               | Y                      |                                                    |
 +----------------------------+---------------------------+------------------------+----------------------------------------------------+

docs/supported_apis/series_supported.rst

@@ -362,7 +362,7 @@ the related section on `Defaulting to pandas`_.
 +-----------------------------+---------------------------------+
 | ``searchsorted``            | Y                               |
 +-----------------------------+---------------------------------+
-| ``sem``                     | D                               |
+| ``sem``                     | Y                               |
 +-----------------------------+---------------------------------+
 | ``set_axis``                | Y                               |
 +-----------------------------+---------------------------------+

modin/backends/base/query_compiler.py

@@ -670,6 +670,18 @@ def skew(self, **kwargs):
         """
         pass
 
+    @abc.abstractmethod
+    def sem(self, **kwargs):
+        """
+        Returns standard deviation of the mean over requested axis.
+
+        Returns
+        -------
+        BaseQueryCompiler
+            QueryCompiler containing the standard deviation of the mean over requested axis.
+        """
+        pass
+
     @abc.abstractmethod
     def std(self, **kwargs):
         """Returns standard deviation of each column or row.

modin/backends/pandas/query_compiler.py

@@ -740,6 +740,7 @@ def sort_index_for_equal_values(result, ascending):
     nunique = ReductionFunction.register(pandas.DataFrame.nunique)
     skew = ReductionFunction.register(pandas.DataFrame.skew)
     kurt = ReductionFunction.register(pandas.DataFrame.kurt)
+    sem = ReductionFunction.register(pandas.DataFrame.sem)
     std = ReductionFunction.register(pandas.DataFrame.std)
     var = ReductionFunction.register(pandas.DataFrame.var)
     sum_min_count = ReductionFunction.register(pandas.DataFrame.sum)

modin/pandas/base.py

@@ -2544,19 +2544,6 @@ def sample(
             query_compiler = self._query_compiler.getitem_row_array(samples)
             return self.__constructor__(query_compiler=query_compiler)
 
-    def sem(
-        self, axis=None, skipna=None, level=None, ddof=1, numeric_only=None, **kwargs
-    ):
-        return self._default_to_pandas(
-            "sem",
-            axis=axis,
-            skipna=skipna,
-            level=level,
-            ddof=ddof,
-            numeric_only=numeric_only,
-            **kwargs,
-        )
-
     def set_axis(self, labels, axis=0, inplace=False):
         """Assign desired index to given axis.
 

modin/pandas/dataframe.py

@@ -2180,6 +2180,59 @@ def is_dtype_instance_mapper(column, dtype):
         ]
         return self.drop(columns=self.columns[indicate], inplace=False)
 
+    def sem(
+        self, axis=None, skipna=None, level=None, ddof=1, numeric_only=None, **kwargs
+    ):
+        """
+        Return unbiased standard error of the mean over requested axis.
+
+        Normalized by N-1 by default. This can be changed using the ddof argument
+
+        Parameters
+        ----------
+            axis : {index (0), columns (1)}
+            skipna : bool, default True
+                Exclude NA/null values. If an entire row/column is NA,
+                the result will be NA.
+            level : int or level name, default None
+                If the axis is a MultiIndex (hierarchical), count along a particular level,
+                collapsing into a Series.
+            ddof : int, default 1
+                Delta Degrees of Freedom. The divisor used in calculations is N - ddof,
+                where N represents the number of elements.
+            numeric_only : bool, default None
+                Include only float, int, boolean columns. If None, will attempt to use everything,
+                then use only numeric data. Not implemented for Series.
+
+        Returns
+        -------
+            Series or DataFrame (if level specified)
+        """
+        axis = self._get_axis_number(axis)
+        if numeric_only is not None and not numeric_only:
+            self._validate_dtypes(numeric_only=True)
+        if level is not None:
+            return self.__constructor__(
+                query_compiler=self._query_compiler.sem(
+                    axis=axis,
+                    skipna=skipna,
+                    level=level,
+                    ddof=ddof,
+                    numeric_only=numeric_only,
+                    **kwargs,
+                )
+            )
+        return self._reduce_dimension(
+            self._query_compiler.sem(
+                axis=axis,
+                skipna=skipna,
+                level=level,
+                ddof=ddof,
+                numeric_only=numeric_only,
+                **kwargs,
+            )
+        )
+
     def set_index(
         self, keys, drop=True, append=False, inplace=False, verify_integrity=False
     ):

modin/pandas/series.py

@@ -1092,6 +1092,59 @@ def nsmallest(self, n=5, keep="first"):
         """
         return Series(query_compiler=self._query_compiler.nsmallest(n=n, keep=keep))
 
+    def sem(
+        self, axis=None, skipna=None, level=None, ddof=1, numeric_only=None, **kwargs
+    ):
+        """
+        Return unbiased standard error of the mean over requested axis.
+
+        Normalized by N-1 by default. This can be changed using the ddof argument
+
+        Parameters
+        ----------
+            axis : {index (0), columns (1)}
+            skipna : bool, default True
+                Exclude NA/null values. If an entire row/column is NA,
+                the result will be NA.
+            level : int or level name, default None
+                If the axis is a MultiIndex (hierarchical), count along a particular level,
+                collapsing into a Series.
+            ddof : int, default 1
+                Delta Degrees of Freedom. The divisor used in calculations is N - ddof,
+                where N represents the number of elements.
+            numeric_only : bool, default None
+                Include only float, int, boolean columns. If None, will attempt to use everything,
+                then use only numeric data. Not implemented for Series.
+
+        Returns
+        -------
+            Scalar or Series (if level specified)
+        """
+        axis = self._get_axis_number(axis)
+        if numeric_only is not None and not numeric_only:
+            self._validate_dtypes(numeric_only=True)
+        if level is not None:
+            return self.__constructor__(
+                query_compiler=self._query_compiler.sem(
+                    axis=axis,
+                    skipna=skipna,
+                    level=level,
+                    ddof=ddof,
+                    numeric_only=numeric_only,
+                    **kwargs,
+                )
+            )
+        return self._reduce_dimension(
+            self._query_compiler.sem(
+                axis=axis,
+                skipna=skipna,
+                level=level,
+                ddof=ddof,
+                numeric_only=numeric_only,
+                **kwargs,
+            )
+        )
+
     def slice_shift(self, periods=1, axis=0):
         """
         Equivalent to `shift` without copying data.

modin/pandas/test/dataframe/test_default.py

@@ -62,7 +62,6 @@
         ("lookup", lambda df: {"row_labels": [0], "col_labels": ["int_col"]}),
         ("mask", lambda df: {"cond": df != 0}),
         ("pct_change", None),
-        ("sem", None),
         ("__getstate__", None),
         ("to_xarray", None),
         ("pivot_table", lambda df: {"values": "int_col", "index": ["float_col"]}),

modin/pandas/test/dataframe/test_window.py

@@ -456,16 +456,16 @@ def test_median_skew_transposed(axis, method):
         ),
     ],
 )
-@pytest.mark.parametrize("method", ["median", "skew", "std", "var", "rank"])
-def test_median_skew_std_var_rank_specific(numeric_only, method):
+@pytest.mark.parametrize("method", ["median", "skew", "std", "var", "rank", "sem"])
+def test_median_skew_std_var_rank_sem_specific(numeric_only, method):
     eval_general(
         *create_test_dfs(test_data_diff_dtype),
         lambda df: getattr(df, method)(numeric_only=numeric_only),
     )
 
 
-@pytest.mark.parametrize("method", ["median", "skew", "std", "var"])
-def test_median_skew_std_var_1953(method):
+@pytest.mark.parametrize("method", ["median", "skew", "std", "var", "sem"])
+def test_median_skew_std_var_sem_1953(method):
     # See #1953 for details
     arrays = [["1", "1", "2", "2"], ["1", "2", "3", "4"]]
     data = [[1, 2, 3, 4], [1, 2, 3, 4], [1, 2, 3, 4], [1, 2, 3, 4]]
@@ -633,11 +633,31 @@ def test_rank_transposed(axis, na_option):
     )
 
 
+@pytest.mark.parametrize(
+    "skipna", bool_arg_values, ids=arg_keys("skipna", bool_arg_keys)
+)
+@pytest.mark.parametrize("ddof", int_arg_values, ids=arg_keys("ddof", int_arg_keys))
+def test_sem_float_nan_only(skipna, ddof):
+    eval_general(
+        *create_test_dfs(test_data["float_nan_data"]),
+        lambda df: df.sem(skipna=skipna, ddof=ddof),
+    )
+
+
+@pytest.mark.parametrize("axis", ["rows", "columns"])
+@pytest.mark.parametrize("ddof", int_arg_values, ids=arg_keys("ddof", int_arg_keys))
+def test_sem_int_only(axis, ddof):
+    eval_general(
+        *create_test_dfs(test_data["int_data"]),
+        lambda df: df.sem(axis=axis, ddof=ddof),
+    )
+
+
 @pytest.mark.parametrize("axis", [0, 1])
 @pytest.mark.parametrize(
     "skipna", bool_arg_values, ids=arg_keys("skipna", bool_arg_keys)
 )
-@pytest.mark.parametrize("method", ["str", "var", "rank"])
+@pytest.mark.parametrize("method", ["std", "var", "rank"])
 def test_std_var_rank(axis, skipna, method):
     eval_general(
         *create_test_dfs(test_data["float_nan_data"]),

modin/pandas/test/test_series.py

@@ -2036,8 +2036,10 @@ def test_median(data, skipna):
     df_equals(modin_series.median(skipna=skipna), pandas_series.median(skipna=skipna))
 
 
-@pytest.mark.parametrize("method", ["median", "skew", "std", "sum", "var", "prod"])
-def test_median_skew_std_sum_var_prod_1953(method):
+@pytest.mark.parametrize(
+    "method", ["median", "skew", "std", "sum", "var", "prod", "sem"]
+)
+def test_median_skew_std_sum_var_prod_sem_1953(method):
     # See #1953 for details
     data = [3, 3, 3, 3, 3, 3, 3, 3, 3]
     arrays = [
@@ -2736,11 +2738,23 @@ def test_searchsorted(
         assert case
 
 
-@pytest.mark.parametrize("data", test_data_values, ids=test_data_keys)
-def test_sem(data):
-    modin_series, _ = create_test_series(data)  # noqa: F841
-    with pytest.warns(UserWarning):
-        modin_series.sem()
+@pytest.mark.parametrize(
+    "skipna", bool_arg_values, ids=arg_keys("skipna", bool_arg_keys)
+)
+@pytest.mark.parametrize("ddof", int_arg_values, ids=arg_keys("ddof", int_arg_keys))
+def test_sem_float_nan_only(skipna, ddof):
+    eval_general(
+        *create_test_series(test_data["float_nan_data"]),
+        lambda df: df.sem(skipna=skipna, ddof=ddof),
+    )
+
+
+@pytest.mark.parametrize("ddof", int_arg_values, ids=arg_keys("ddof", int_arg_keys))
+def test_sem_int_only(ddof):
+    eval_general(
+        *create_test_series(test_data["int_data"]),
+        lambda df: df.sem(ddof=ddof),
+    )
 
 
 @pytest.mark.parametrize("data", test_data_values, ids=test_data_keys)