[SPARK-7548] [SQL] Add explode function for DataFrames

Add an `explode` function for dataframes and modify the analyzer so that single table generating functions can be present in a select clause along with other expressions.   There are currently the following restrictions:
 - only top level TGFs are allowed (i.e. no `select(explode('list) + 1)`)
 - only one may be present in a single select to avoid potentially confusing implicit Cartesian products.

TODO:
 - [ ] Python

Author: Michael Armbrust <michael@databricks.com>

Closes #6107 from marmbrus/explodeFunction and squashes the following commits:

7ee2c87 [Michael Armbrust] whitespace
6f80ba3 [Michael Armbrust] Update dataframe.py
c176c89 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into explodeFunction
81b5da3 [Michael Armbrust] style
d3faa05 [Michael Armbrust] fix self join case
f9e1e3e [Michael Armbrust] fix python, add since
4f0d0a9 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into explodeFunction
e710fe4 [Michael Armbrust] add java and python
52ca0dc [Michael Armbrust] [SPARK-7548][SQL] Add explode function for dataframes.

1 files changed, 20 insertions, 0 deletions

diff --git a/python/pyspark/sql/functions.py b/python/pyspark/sql/functions.py
index d91265ee0b..6cd6974b0e 100644
--- a/python/pyspark/sql/functions.py
+++ b/python/pyspark/sql/functions.py
@@ -169,6 +169,26 @@ def approxCountDistinct(col, rsd=None):
     return Column(jc)
 
 
+def explode(col):
+    """Returns a new row for each element in the given array or map.
+
+    >>> from pyspark.sql import Row
+    >>> eDF = sqlContext.createDataFrame([Row(a=1, intlist=[1,2,3], mapfield={"a": "b"})])
+    >>> eDF.select(explode(eDF.intlist).alias("anInt")).collect()
+    [Row(anInt=1), Row(anInt=2), Row(anInt=3)]
+
+    >>> eDF.select(explode(eDF.mapfield).alias("key", "value")).show()
+    +---+-----+
+    |key|value|
+    +---+-----+
+    |  a|    b|
+    +---+-----+
+    """
+    sc = SparkContext._active_spark_context
+    jc = sc._jvm.functions.explode(_to_java_column(col))
+    return Column(jc)
+
+
 def coalesce(*cols):
     """Returns the first column that is not null.