Let's suppose to have:
df = pd.DataFrame({'key': ['a','b','b','c','c'], 'x': [1,2,3,4,5]})
This dataframe:
key x
0 a 1
1 b 2
2 b 3
3 c 4
4 c 5
has one 'a' row, two 'b' rows and two 'c' rows.
Now if I group the dataframe by key column and apply a function f printing out the name of each grouped dataframe I have:
df.groupby('key').apply(lambda x: print(x.name))
with this output:
a
a
b
c
Out[71]:
Empty DataFrame
Columns: []
Index: []
why there are two prints of a?
Note my pandas version is 0.20.1
pd.__version__
Out[72]: '0.20.1'
