Expose half_up rounding in cuDF (#8477)

Authors:
  - Ashwin Srinath (https://github.com/shwina)

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Ram (Ramakrishna Prabhu) (https://github.com/rgsl888prabhu)
  - Michael Wang (https://github.com/isVoid)
  - Marlene  (https://github.com/marlenezw)

URL: #8477

python/cudf/cudf/_lib/round.pyx

@@ -13,7 +13,7 @@ from cudf._lib.cpp.round cimport (
 )
 
 
-def round(Column input_col, int decimal_places=0):
+def round(Column input_col, int decimal_places=0, how="half_even"):
     """
     Round column values to the given number of decimal places
 
@@ -26,16 +26,21 @@ def round(Column input_col, int decimal_places=0):
     -------
     A Column with values rounded to the given number of decimal places
     """
+    if how not in {"half_even", "half_up"}:
+        raise ValueError("'how' must be either 'half_even' or 'half_up'")
 
     cdef column_view input_col_view = input_col.view()
     cdef unique_ptr[column] c_result
-
+    cdef cpp_rounding_method c_how = (
+        cpp_rounding_method.HALF_EVEN if how == "half_even"
+        else cpp_rounding_method.HALF_UP
+    )
     with nogil:
         c_result = move(
             cpp_round(
                 input_col_view,
                 decimal_places,
-                cpp_rounding_method.HALF_EVEN,
+                c_how
             )
         )
 

python/cudf/cudf/core/column/numerical_base.py

@@ -191,10 +191,12 @@ def corr(self, other: ColumnBase) -> float:
             return cudf.utils.dtypes._get_nan_for_dtype(self.dtype)
         return cov / lhs_std / rhs_std
 
-    def round(self, decimals: int = 0) -> NumericalBaseColumn:
+    def round(
+        self, decimals: int = 0, how: str = "half_even"
+    ) -> NumericalBaseColumn:
         """Round the values in the Column to the given number of decimals.
         """
-        return libcudf.round.round(self, decimal_places=decimals)
+        return libcudf.round.round(self, decimal_places=decimals, how=how)
 
     def _apply_scan_op(self, op: str) -> ColumnBase:
         return self._copy_type_metadata(libcudf.reduce.scan(op, self, True))

python/cudf/cudf/core/frame.py

@@ -1661,7 +1661,7 @@ def __arrow_array__(self, type=None):
             "consider using .to_arrow()"
         )
 
-    def round(self, decimals=0):
+    def round(self, decimals=0, how="half_even"):
         """
         Round a DataFrame to a variable number of decimal places.
 
@@ -1676,6 +1676,9 @@ def round(self, decimals=0):
             columns not included in `decimals` will be left as is. Elements
             of `decimals` which are not columns of the input will be
             ignored.
+        how : str, optional
+            Type of rounding. Can be either "half_even" (default)
+            of "half_up" rounding.
 
         Returns
         -------
@@ -1741,7 +1744,7 @@ def round(self, decimals=0):
                 raise ValueError("Index of decimals must be unique")
 
             cols = {
-                name: col.round(decimals[name])
+                name: col.round(decimals[name], how=how)
                 if (
                     name in decimals.keys()
                     and pd.api.types.is_numeric_dtype(col.dtype)
@@ -1751,7 +1754,7 @@ def round(self, decimals=0):
             }
         elif isinstance(decimals, int):
             cols = {
-                name: col.round(decimals)
+                name: col.round(decimals, how=how)
                 if pd.api.types.is_numeric_dtype(col.dtype)
                 else col.copy(deep=True)
                 for name, col in self._data.items()

python/cudf/cudf/core/series.py

@@ -4748,7 +4748,7 @@ def mode(self, dropna=True):
 
         return Series(val_counts.index.sort_values(), name=self.name)
 
-    def round(self, decimals=0):
+    def round(self, decimals=0, how="half_even"):
         """
         Round each value in a Series to the given number of decimals.
 
@@ -4758,6 +4758,9 @@ def round(self, decimals=0):
             Number of decimal places to round to. If decimals is negative,
             it specifies the number of positions to the left of the decimal
             point.
+        how : str, optional
+            Type of rounding. Can be either "half_even" (default)
+            of "half_up" rounding.
 
         Returns
         -------
@@ -4773,9 +4776,8 @@ def round(self, decimals=0):
         2    3.0
         dtype: float64
         """
-
         return Series(
-            self._column.round(decimals=decimals),
+            self._column.round(decimals=decimals, how=how),
             name=self.name,
             index=self.index,
             dtype=self.dtype,

python/cudf/cudf/tests/test_series.py

@@ -692,6 +692,13 @@ def test_series_round(arr, decimals):
     np.array_equal(ser.nullmask.to_array(), result.to_array())
 
 
+def test_series_round_half_up():
+    s = cudf.Series([0.0, 1.0, 1.2, 1.7, 0.5, 1.5, 2.5, None])
+    expect = cudf.Series([0.0, 1.0, 1.0, 2.0, 1.0, 2.0, 3.0, None])
+    got = s.round(how="half_up")
+    assert_eq(expect, got)
+
+
 @pytest.mark.parametrize(
     "series",
     [