[SPARK-5678] Convert DataFrame to pandas.DataFrame and Series

```
pyspark.sql.DataFrame.to_pandas = to_pandas(self) unbound pyspark.sql.DataFrame method
    Collect all the rows and return a `pandas.DataFrame`.

    >>> df.to_pandas()  # doctest: +SKIP
       age   name
    0    2  Alice
    1    5    Bob

pyspark.sql.Column.to_pandas = to_pandas(self) unbound pyspark.sql.Column method
    Return a pandas.Series from the column

    >>> df.age.to_pandas()  # doctest: +SKIP
    0    2
    1    5
    dtype: int64
```

Not tests by jenkins (they depends on pandas)

Author: Davies Liu <davies@databricks.com>

Closes #4476 from davies/to_pandas and squashes the following commits:

6276fb6 [Davies Liu] Convert DataFrame to pandas.DataFrame and Series

1 files changed, 25 insertions, 0 deletions

diff --git a/python/pyspark/sql.py b/python/pyspark/sql.py
index e55f285a77..6a6dfbc585 100644
--- a/python/pyspark/sql.py
+++ b/python/pyspark/sql.py
@@ -2284,6 +2284,18 @@ class DataFrame(object):
         """
         return self.select('*', col.alias(colName))
 
+    def to_pandas(self):
+        """
+        Collect all the rows and return a `pandas.DataFrame`.
+
+        >>> df.to_pandas()  # doctest: +SKIP
+           age   name
+        0    2  Alice
+        1    5    Bob
+        """
+        import pandas as pd
+        return pd.DataFrame.from_records(self.collect(), columns=self.columns)
+
 
 # Having SchemaRDD for backward compatibility (for docs)
 class SchemaRDD(DataFrame):
@@ -2551,6 +2563,19 @@ class Column(DataFrame):
             jc = self._jc.cast(jdt)
         return Column(jc, self.sql_ctx)
 
+    def to_pandas(self):
+        """
+        Return a pandas.Series from the column
+
+        >>> df.age.to_pandas()  # doctest: +SKIP
+        0    2
+        1    5
+        dtype: int64
+        """
+        import pandas as pd
+        data = [c for c, in self.collect()]
+        return pd.Series(data)
+
 
 def _aggregate_func(name, doc=""):
     """ Create a function for aggregator by name"""