Test plan

databricks/koalas/frame.py

@@ -4008,6 +4008,63 @@ def duplicated(self, subset=None, keep="first") -> "Series":
             )
         )
 
+    def dot(self, other: "Series") -> "Series":
+        """
+        Compute the matrix multiplication between the DataFrame and other.
+
+        This method computes the matrix product between the DataFrame and the
+        values of an other Series
+
+        It can also be called using ``self @ other`` in Python >= 3.5.
+
+        Parameters
+        ----------
+        other : Series
+            The other object to compute the matrix product with.
+
+        Returns
+        -------
+        Series
+            Return the matrix product between self and other as a Series.
+
+        See Also
+        --------
+        Series.dot: Similar method for Series.
+
+        Notes
+        -----
+        The dimensions of DataFrame and other must be compatible in order to
+        compute the matrix multiplication. In addition, the column names of
+        DataFrame and the index of other must contain the same values, as they
+        will be aligned prior to the multiplication.
+
+        The dot method for Series computes the inner product, instead of the
+        matrix product here.
+
+        Examples
+        --------
+        >>> from databricks.koalas.config import set_option, reset_option
+        >>> set_option("compute.ops_on_diff_frames", True)
+        >>> kdf = ks.DataFrame([[0, 1, -2, -1], [1, 1, 1, 1]])
+        >>> kser = ks.Series([1, 1, 2, 1])
+        >>> kdf.dot(kser)
+        0   -4
+        1    5
+        dtype: int64
+
+        Note how shuffling of the objects does not change the result.
+
+        >>> kser2 = kser.reindex([1, 0, 2, 3])
+        >>> kdf.dot(kser2)
+        0   -4
+        1    5
+        dtype: int64
+        """
+        if not isinstance(other, ks.Series):
+            raise TypeError("Unsupported type {}".format(type(other).__name__))
+        else:
+            return other.dot(self.transpose()).rename(None)
+
     def to_koalas(self, index_col: Optional[Union[str, List[str]]] = None) -> "DataFrame":
         """
         Converts the existing DataFrame into a Koalas DataFrame.

databricks/koalas/tests/test_ops_on_diff_frames.py

@@ -917,6 +917,57 @@ def test_dot(self):
         pdf = kdf.to_pandas()
         self.assert_eq(kser.dot(kdf), pser.dot(pdf))
 
+    def test_frame_dot(self):
+        pdf = pd.DataFrame([[0, 1, -2, -1], [1, 1, 1, 1]])
+        kdf = ks.from_pandas(pdf)
+
+        pser = pd.Series([1, 1, 2, 1])
+        kser = ks.from_pandas(pser)
+        self.assert_eq(kdf.dot(kser), pdf.dot(pser))
+
+        # Index reorder
+        pser = pser.reindex([1, 0, 2, 3])
+        kser = ks.from_pandas(pser)
+        self.assert_eq(kdf.dot(kser), pdf.dot(pser))
+
+        # ser with name
+        pser.name = "ser"
+        kser = ks.from_pandas(pser)
+        self.assert_eq(kdf.dot(kser), pdf.dot(pser))
+
+        # df with MultiIndex as column (ser with MultiIndex)
+        arrays = [[1, 1, 2, 2], ["red", "blue", "red", "blue"]]
+        pidx = pd.MultiIndex.from_arrays(arrays, names=("number", "color"))
+        pser = pd.Series([1, 1, 2, 1], index=pidx)
+        pdf = pd.DataFrame([[0, 1, -2, -1], [1, 1, 1, 1]], columns=pidx)
+        kdf = ks.from_pandas(pdf)
+        kser = ks.from_pandas(pser)
+        self.assert_eq(kdf.dot(kser), pdf.dot(pser))
+
+        # df with Index as column (ser with Index)
+        pidx = pd.Index([1, 2, 3, 4], name="number")
+        pser = pd.Series([1, 1, 2, 1], index=pidx)
+        pdf = pd.DataFrame([[0, 1, -2, -1], [1, 1, 1, 1]], columns=pidx)
+        kdf = ks.from_pandas(pdf)
+        kser = ks.from_pandas(pser)
+        self.assert_eq(kdf.dot(kser), pdf.dot(pser))
+
+        # df with Index
+        pdf.index = pd.Index(["x", "y"], name="char")
+        kdf = ks.from_pandas(pdf)
+        self.assert_eq(kdf.dot(kser), pdf.dot(pser))
+
+        # df with MultiIndex
+        pdf.index = pd.MultiIndex.from_arrays([[1, 1], ["red", "blue"]], names=("number", "color"))
+        kdf = ks.from_pandas(pdf)
+        self.assert_eq(kdf.dot(kser), pdf.dot(pser))
+
+        pdf = pd.DataFrame([[1, 2], [3, 4]])
+        kdf = ks.from_pandas(pdf)
+        self.assert_eq(kdf.dot(kdf[0]), pdf.dot(pdf[0]))
+        self.assert_eq(kdf.dot(kdf[0] * 10), pdf.dot(pdf[0] * 10))
+        self.assert_eq((kdf + 1).dot(kdf[0] * 10), (pdf + 1).dot(pdf[0] * 10))
+
     def test_to_series_comparison(self):
         kidx1 = ks.Index([1, 2, 3, 4, 5])
         kidx2 = ks.Index([1, 2, 3, 4, 5])