pandas get mean column name and extra string columns - python-2.7

Question

In pandas 0.18.1, python 2.7.6:
Imagine we have the following table:
ID,FROM_YEAR,FROM_MONTH,AREA
1,2015,1,200
1,2015,2,200
1,2015,3,200
1,2015,4,200
1,2015,5,200
1,2015,6,200
1,2015,7,200
1,2015,8,200
1,2015,9,200
1,2015,10,200
1,2015,11,200
1,2015,12,200
1,2016,1,100
1,2016,2,100
1,2016,3,100
1,2016,4,100
1,2016,5,100
1,2016,6,100
1,2016,7,100
1,2016,8,100
1,2016,9,100
1,2016,10,100
1,2016,11,100
1,2016,12,100
We are trying to get an calendar year average in the following format
ID,FROM_YEAR,TYPE,AREA
1,2015,A,200
1,2016,A,100
1,2015,B,200
1,2016,B,100
Note: TYPE is a string column for other information. Here we only have 2 types of 'TYPE': 'A' and 'B'
If we tried the following, the 'AREA' column name is missing, also the ID=1 only shows in the first case.
AREA_CY=df.groupby(['ID','FROM_YEAR'])['AREA'].mean()
it returns:
ID,FROM_YEAR,
1,2015,200
,2016,100
,2015,200
,2016,100
If we tried the following:
AREA_CY=df.groupby(['ID','FROM_YEAR'])['AREA'].mean(axis=1)
it returns:
TypeError: mean() got an unexpected keyword argument 'axis'
Could any guru enlighten? Thanks!

Answer 1

Try this:
In [102]: x = df.groupby(['ID','FROM_YEAR'])['AREA'].mean().reset_index(name='AREA')
In [103]: y = pd.DataFrame({'TYPE':['A','B']})
In [104]: x
Out[104]:
ID FROM_YEAR AREA
0 1 2015 200
1 1 2016 100
In [105]: y
Out[105]:
TYPE
0 A
1 B
In [106]: x.assign(key=0).merge(y.assign(key=0), on='key').drop('key', 1)
Out[106]:
ID FROM_YEAR AREA TYPE
0 1 2015 200 A
1 1 2015 200 B
2 1 2016 100 A
3 1 2016 100 B
Explanation:
Let's make a cartesian product (AKA full outer join) of x and y DFs:
In [126]: x.assign(key=0)
Out[126]:
ID FROM_YEAR AREA key
0 1 2015 200 0
1 1 2016 100 0
In [127]: y.assign(key=0)
Out[127]:
TYPE key
0 A 0
1 B 0
In [128]: x.assign(key=0).merge(y.assign(key=0), on='key')
Out[128]:
ID FROM_YEAR AREA key TYPE
0 1 2015 200 0 A
1 1 2015 200 0 B
2 1 2016 100 0 A
3 1 2016 100 0 B