grundprinzip commented on code in PR #38631:
URL: https://github.com/apache/spark/pull/38631#discussion_r1020586736
##########
python/pyspark/sql/connect/column.py:
##########
@@ -82,6 +82,74 @@ def to_plan(self, session: "RemoteSparkSession") ->
"proto.Expression":
def __str__(self) -> str:
...
+ def alias(self, *alias: str, **kwargs: Any) -> "Expression":
+ """
+ Returns this column aliased with a new name or names (in the case of
expressions that
+ return more than one column, such as explode).
+
+ .. versionadded:: 1.3.0
+
+ Parameters
+ ----------
+ alias : str
+ desired column names (collects all positional arguments passed)
+
+ Other Parameters
+ ----------------
+ metadata: dict
+ a dict of information to be stored in ``metadata`` attribute of the
+ corresponding :class:`StructField <pyspark.sql.types.StructField>`
(optional, keyword
+ only argument)
+
+ .. versionchanged:: 2.2.0
+ Added optional ``metadata`` argument.
+
+ Returns
+ -------
+ :class:`Column`
+ Column representing whether each element of Column is aliased with
new name or names.
+
+ Examples
+ --------
+ >>> df = spark.createDataFrame(
+ ... [(2, "Alice"), (5, "Bob")], ["age", "name"])
+ >>> df.select(df.age.alias("age2")).collect()
+ [Row(age2=2), Row(age2=5)]
+ >>> df.select(df.age.alias("age3", metadata={'max':
99})).schema['age3'].metadata['max']
+ 99
+ """
+ metadata = kwargs.pop("metadata", None)
+ assert not kwargs, "Unexpected kwargs where passed: %s" % kwargs
+ return ColumnAlias(self, list(alias), metadata)
+
+
+class ColumnAlias(Expression):
+ def __init__(self, parent: Expression, alias: list[str], metadata: Any):
+
+ self._alias = alias
+ self._metadata = metadata
+ self._parent = parent
+
+ def to_plan(self, session: "RemoteSparkSession") -> "proto.Expression":
+ if len(self._alias) == 1:
+ if self._metadata:
+ raise ValueError("Creating aliases with metadata is not
supported.")
+ else:
+ exp = proto.Expression()
+ exp.alias.name.append(self._alias[0])
+ exp.alias.expr.CopyFrom(self._parent.to_plan(session))
+ return exp
+ else:
+ if self._metadata:
+ raise ValueError("metadata can only be provided for a single
column")
Review Comment:
I just pushed the implementation of metadata as well. However, now the
schema does not return the metadata, but at least the input is consistent with
Spark.
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