Add bigframes.bigquery.rand() function

This change adds `bigframes.bigquery.rand()` which wraps the BigQuery `RAND()` function.
It accepts a Series or DataFrame as input to determine the shape and index of the output Series.
It includes a warning about non-determinism in the docstring.

Additionally, `SqlScalarOp` has been updated to accept an `is_deterministic` argument, which is set to `False` for `rand()`.

Tests are added in `tests/unit/bigquery/test_mathematical.py` and `tests/system/small/bigquery/test_mathematical.py`.

Author: google-labs-jules[bot]

bigframes/bigquery/_operations/mathematical.py

@@ -16,7 +16,8 @@
 
 from typing import Union
 
-from bigframes import dataframe, dtypes
+from bigframes import dataframe
+from bigframes import dtypes
 from bigframes import operations as ops
 from bigframes import series
 
@@ -62,5 +63,6 @@ def rand(input_data: Union[series.Series, dataframe.DataFrame]) -> series.Series
     op = ops.SqlScalarOp(
         _output_type=dtypes.FLOAT_DTYPE,
         sql_template="RAND()",
+        is_deterministic=False,
     )
     return anchor._apply_nary_op(op, [])

bigframes/operations/generic_ops.py

@@ -443,10 +443,15 @@ class SqlScalarOp(base_ops.NaryOp):
     name: typing.ClassVar[str] = "sql_scalar"
     _output_type: dtypes.ExpressionType
     sql_template: str
+    is_deterministic: bool = True
 
     def output_type(self, *input_types: dtypes.ExpressionType) -> dtypes.ExpressionType:
         return self._output_type
 
+    @property
+    def deterministic(self) -> bool:
+        return self.is_deterministic
+
 
 @dataclasses.dataclass(frozen=True)
 class PyUdfOp(base_ops.NaryOp):

tests/unit/bigquery/test_mathematical.py

@@ -32,6 +32,7 @@ def test_rand_calls_apply_nary_op():
     assert isinstance(op, ops.SqlScalarOp)
     assert op.sql_template == "RAND()"
     assert op._output_type == dtypes.FLOAT_DTYPE
+    assert op.deterministic is False
     assert args[1] == []