[GitHub] [spark] zhengruifeng commented on a diff in pull request #37978: [SPARK-40330][PS] Implement `Series.searchsorted`

[GitBox <gi...@apache.org>]

zhengruifeng commented on code in PR #37978:
URL: https://github.com/apache/spark/pull/37978#discussion_r979482634


##########
python/pyspark/pandas/series.py:
##########
@@ -6610,6 +6610,78 @@ def compare(
         )
         return DataFrame(internal)
 
+    # todo: 1, support array-like 'value'; 2, add parameter 'sorter'
+    def searchsorted(self, value: Any, side: str = "left") -> int:
+        """
+        Find indices where elements should be inserted to maintain order.
+
+        Find the indices into a sorted Series self such that, if the corresponding elements
+        in value were inserted before the indices, the order of self would be preserved.
+
+        Parameters
+        ----------
+        value : scalar
+            Values to insert into self.
+        side : {‘left’, ‘right’}, optional
+            If ‘left’, the index of the first suitable location found is given.
+            If ‘right’, return the last such index. If there is no suitable index,
+            return either 0 or N (where N is the length of self).
+
+        Returns
+        -------
+        int
+            insertion point
+
+        Notes
+        -----
+        The Series must be monotonically sorted, otherwise wrong locations will likely be returned.
+
+        Examples
+        --------
+        >>> ser = ps.Series([1, 2, 2, 3])
+        >>> ser.searchsorted(0)
+        0
+        >>> ser.searchsorted(1)
+        0
+        >>> ser.searchsorted(2)
+        1
+        >>> ser.searchsorted(5)
+        4
+        >>> ser.searchsorted(0, side="right")
+        0
+        >>> ser.searchsorted(1, side="right")
+        1
+        >>> ser.searchsorted(2, side="right")
+        3
+        >>> ser.searchsorted(5, side="right")
+        4
+        """
+        if side not in ["left", "right"]:
+            raise ValueError(f"Invalid side {side}")
+
+        sdf = self._internal.spark_frame
+        index_col_name = verify_temp_column_name(sdf, "__search_sorted_index_col__")
+        value_col_name = verify_temp_column_name(sdf, "__search_sorted_value_col__")
+        sdf = InternalFrame.attach_distributed_sequence_column(
+            sdf.select(self.spark.column.alias(value_col_name)), index_col_name
+        )
+
+        if side == "left":
+            results = sdf.select(
+                F.min(F.when(F.lit(value) <= F.col(value_col_name), F.col(index_col_name))),
+                F.count(F.lit(0)),
+            ).take(1)
+        else:
+            results = sdf.select(
+                F.min(F.when(F.lit(value) < F.col(value_col_name), F.col(index_col_name))),
+                F.count(F.lit(0)),
+            ).take(1)

Review Comment:
   ```
   In [5]: ser = pd.Series([])
   <ipython-input-5-2e6ace2afa48>:1: FutureWarning: The default dtype for empty Series will be 'object' instead of 'float64' in a future version. Specify a dtype explicitly to silence this warning.
     ser = pd.Series([])
   
   In [6]: ser.searchsorted(5, 'right')
   Out[6]: 0
   ```
   
   `Series.searchsorted` works with empty series, so here should use `take` instead of `first` which will raise an exception.
   
   Let me add a test case for empty series



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