Merge remote-tracking branch 'upstream/master' into series_drop

Author: itholic

.gitignore

@@ -51,3 +51,8 @@ _build
 
 # Spark
 spark-warehouse/
+
+# Pypandoc
+pandoc*
+whatsnew
+

.travis.yml

@@ -36,7 +36,7 @@ matrix:
         - PATH=$(echo "$PATH" | sed -e 's/:\/usr\/local\/lib\/jvm\/openjdk11\/bin//')
         - JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-amd64
         - SPARK_VERSION=2.4.4
-        - PANDAS_VERSION=0.25.0
+        - PANDAS_VERSION=0.25.1
         - PYARROW_VERSION=0.13.0
 
 before_install:

README.md

@@ -10,6 +10,9 @@ pandas is the de facto standard (single-node) DataFrame implementation in Python
 
 This project is currently in beta and is rapidly evolving, with a weekly release cadence. We would love to have you try it and give us feedback, through our [mailing lists](https://groups.google.com/forum/#!forum/koalas-dev) or [GitHub issues](https://github.com/databricks/koalas/issues).
 
+Try the Koalas 10 minutes tutorial on a live notebook in Jupyter here [![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/databricks/koalas/master?filepath=docs%2Fsource%2Fgetting_started%2F10min.ipynb)
+. The initial launch can take up to several minutes.
+
 [![Build Status](https://travis-ci.com/databricks/koalas.svg?token=Rzzgd1itxsPZRuhKGnhD&branch=master)](https://travis-ci.com/databricks/koalas)
 [![codecov](https://codecov.io/gh/databricks/koalas/branch/master/graph/badge.svg)](https://codecov.io/gh/databricks/koalas)
 [![Documentation Status](https://readthedocs.org/projects/koalas/badge/?version=latest)](https://koalas.readthedocs.io/en/latest/?badge=latest)

databricks/koalas/frame.py

@@ -34,6 +34,7 @@
 from databricks.koalas.indexing import AtIndexer, ILocIndexer, LocIndexer
 from databricks.koalas.internal import _InternalFrame
 from databricks.koalas.utils import validate_arguments_and_invoke_function
+from databricks.koalas.window import Rolling, Expanding
 
 
 class _Frame(object):
@@ -1255,11 +1256,13 @@ def groupby(self, by, as_index: bool = True):
 
         df_or_s = self
         if isinstance(by, str):
+            by = [(by,)]
+        elif isinstance(by, tuple):
             by = [by]
         elif isinstance(by, Series):
             by = [by]
         elif isinstance(by, Iterable):
-            by = list(by)
+            by = [key if isinstance(key, (tuple, Series)) else (key,) for key in by]
         else:
             raise ValueError('Not a valid index: TODO')
         if not len(by):
@@ -1384,6 +1387,12 @@ def median(self, accuracy=10000):
         # This is expected to be small so it's fine to transpose.
         return DataFrame(sdf)._to_internal_pandas().transpose().iloc[:, 0]
 
+    def rolling(self, *args, **kwargs):
+        return Rolling(self)
+
+    def expanding(self, *args, **kwargs):
+        return Expanding(self)
+
     @property
     def at(self):
         return AtIndexer(self)
@@ -1421,7 +1430,7 @@ def _resolve_col(kdf, col_like):
         assert kdf is col_like._kdf, \
             "Cannot combine column argument because it comes from a different dataframe"
         return col_like
-    elif isinstance(col_like, str):
+    elif isinstance(col_like, tuple):
         return kdf[col_like]
     else:
         raise ValueError(col_like)