1 files changed, 24 insertions, 2 deletions
diff --git a/python/pyspark/sql/functions.py b/python/pyspark/sql/functions.py
index 38a043a3c5..d91265ee0b 100644
--- a/python/pyspark/sql/functions.py
+++ b/python/pyspark/sql/functions.py
@@ -32,13 +32,14 @@ from pyspark.sql.dataframe import Column, _to_java_column, _to_seq
 
 __all__ = [
     'approxCountDistinct',
+    'coalesce',
     'countDistinct',
     'monotonicallyIncreasingId',
     'rand',
     'randn',
     'sparkPartitionId',
-    'coalesce',
-    'udf']
+    'udf',
+    'when']
 
 
 def _create_function(name, doc=""):
@@ -291,6 +292,27 @@ def struct(*cols):
     return Column(jc)
 
 
+def when(condition, value):
+    """Evaluates a list of conditions and returns one of multiple possible result expressions.
+    If :func:`Column.otherwise` is not invoked, None is returned for unmatched conditions.
+
+    :param condition: a boolean :class:`Column` expression.
+    :param value: a literal value, or a :class:`Column` expression.
+
+    >>> df.select(when(df['age'] == 2, 3).otherwise(4).alias("age")).collect()
+    [Row(age=3), Row(age=4)]
+
+    >>> df.select(when(df.age == 2, df.age + 1).alias("age")).collect()
+    [Row(age=3), Row(age=None)]
+    """
+    sc = SparkContext._active_spark_context
+    if not isinstance(condition, Column):
+        raise TypeError("condition should be a Column")
+    v = value._jc if isinstance(value, Column) else value
+    jc = sc._jvm.functions.when(condition._jc, v)
+    return Column(jc)
+
+
 class UserDefinedFunction(object):
     """
     User defined function in Python