From 1168273efa0f941eae734645dc2d3d82ae778016 Mon Sep 17 00:00:00 2001
From: Tom Augspurger <tom.w.augspurger@gmail.com>
Date: Mon, 17 Sep 2018 20:48:23 -0500
Subject: [PATCH] FutureWarning from groupby.

Warning about elementwise comparison failing when we indexed
a dataframe with boolean dataframe
---
 doc/source/cookbook.rst | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/doc/source/cookbook.rst b/doc/source/cookbook.rst
index f6fa9e9f86143..a4dc99383a562 100644
--- a/doc/source/cookbook.rst
+++ b/doc/source/cookbook.rst
@@ -505,13 +505,11 @@ Unlike agg, apply's callable is passed a sub-DataFrame which gives you access to
 .. ipython:: python
 
    df = pd.DataFrame({'A' : [1, 1, 2, 2], 'B' : [1, -1, 1, 2]})
-
    gb = df.groupby('A')
 
    def replace(g):
-      mask = g < 0
-      g.loc[mask] = g[~mask].mean()
-      return g
+       mask = g < 0
+       return g.where(mask, g[~mask].mean())
 
    gb.transform(replace)