Implement DataFrame diff()

python/cudf/cudf/core/dataframe.py

@@ -2633,6 +2633,64 @@ def insert(self, loc, name, value):
 
         self._data.insert(name, value, loc=loc)
 
+    def diff(self, periods=1, axis=0):
+        """
+        Calculates the difference of a Dataframe element compared with
+        another element in the Dataframe, treating each column independently
+
+        Parameters
+        ----------
+        periods : int, default 1
+            Periods to shift for calculating difference,
+            accepts negative values.
+        axis : {0 or ‘index’, 1 or ‘columns’}, default 0
+            Take difference over rows (0) or columns (1).
+            Only row-wise (0) shift is supported.
+
+        Returns
+        -------
+        DataFrame
+            First differences of the DataFrame.
+
+        Notes
+        -----
+        Diff currently only supports numeric dtype columns
+
+        Examples
+        --------
+        >>> import cudf
+        >>> gdf = cudf.DataFrame({'a': [1, 2, 3, 4, 5, 6],
+                                  'b': [1, 1, 2, 3, 5, 8],
+                                  'c': [1, 4, 9, 16, 25, 36]})
+        >>> gdf
+        a  b   c
+        0  1  1   1
+        1  2  1   4
+        2  3  2   9
+        3  4  3  16
+        4  5  5  25
+        5  6  8  36
+        >>> gdf.diff(periods=2)
+            a     b     c
+        0  <NA>  <NA>  <NA>
+        1  <NA>  <NA>  <NA>
+        2     2     1     8
+        3     2     2    12
+        4     2     3    16
+        5     2     5    20
+
+        """
+
+        if not axis == 0:
+            raise NotImplementedError("Only axis=0 is supported.")
+
+        if not all(is_numeric_dtype(i) for i in self.dtypes):
+            raise NotImplementedError(
+                "Diff currently only supports numeric dtypes"
+            )
+
+        return self - self.shift(periods=periods)
+
     def drop(
         self,
         labels=None,

python/cudf/cudf/tests/test_dataframe.py

@@ -9059,3 +9059,71 @@ def test_dataframe_add_suffix():
     expected = pdf.add_suffix("_item")
 
     assert_eq(got, expected)
+
+
+@pytest.mark.parametrize(
+    "data",
+    [
+        np.random.randint(-50, 50, (25, 30)),
+        np.random.random_sample((4, 4)),
+        np.array([1.123, 2.343, 5.890, 0.0]),
+        [np.nan, None, np.nan, None],
+        [True, False, True, False, False],
+        {"a": [1.123, 2.343, np.nan, np.nan], "b": [None, 3, 9.08, None]},
+    ],
+)
+@pytest.mark.parametrize("periods", range(-4, 5))
+def test_diff_dataframe_numeric_dtypes(data, periods):
+    gdf = cudf.DataFrame(data)
+    pdf = gdf.to_pandas()
+
+    actual = gdf.diff(periods=periods, axis=0)
+    expected = pdf.diff(periods=periods, axis=0)
+
+    assert_eq(
+        expected, actual, check_dtype=False,
+    )
+
+
+@pytest.mark.parametrize(
+    ("precision", "scale"), [(5, 2), (4, 3), (8, 5), (3, 1), (6, 4)],
+)
+def test_diff_decimal64_dtype(precision, scale):
+    gdf = cudf.DataFrame(
+        np.random.uniform(10.5, 75.5, (10, 6)),
+        dtype=cudf.Decimal64Dtype(precision=precision, scale=scale),
+    )
+    pdf = gdf.to_pandas()
+
+    actual = gdf.diff()
+    expected = pdf.diff()
+
+    assert_eq(
+        expected, actual, check_dtype=False,
+    )
+
+
+def test_diff_dataframe_invalid_axis():
+    with pytest.raises(NotImplementedError, match="Only axis=0 is supported."):
+        gdf = cudf.DataFrame(np.random.random_sample((4, 4)))
+        gdf.diff(periods=1, axis=1)
+
+
+@pytest.mark.parametrize(
+    "data",
+    [
+        {
+            "int_col": [1, 2, 3, 4, 5],
+            "float_col": [1.0, 2.0, 3.0, 4.0, 5.0],
+            "string_col": ["a", "b", "c", "d", "e"],
+        },
+        ["a", "b", "c", "d", "e"],
+    ],
+)
+def test_diff_dataframe_non_numeric_dypes(data):
+    with pytest.raises(
+        NotImplementedError,
+        match="Diff currently only supports numeric dtypes",
+    ):
+        gdf = cudf.DataFrame(data)
+        gdf.diff(periods=2, axis=0)