pandas dataframe with 2-rows header and export to csv

Question

I have a dataframe

df = pd.DataFrame(columns = [\"AA\", \"BB\", \"CC\"])
df.loc[0]= [\"a\", \"b\", \"c1\"]
df.loc[1]= [\"a\", \"b\", \"c2\"]
df.loc[2]= [\"a\         


        

Answer 1

I think this is a bug in to_csv. If you're looking for workarounds then here's a couple.

To read back in this csv specify the header rows*:

In [11]: csv = "AA,BB,CC
DD,EE,FF
,,
a,b,c1
a,b,c2
a,b,c3"

In [12]: pd.read_csv(StringIO(csv), header=[0, 1])
Out[12]:
  AA BB  CC
  DD EE  FF
0  a  b  c1
1  a  b  c2
2  a  b  c3

*strangely this seems to ignore the blank lines.

To write out you could write the header first and then append:

with open('test.csv', 'w') as f:
    f.write('\n'.join([','.join(h) for h in zip(*df.columns)]) + '\n')
df.to_csv('test.csv', mode='a', index=False, header=False)

Note the to_csv part for MultiIndex column here:

In [21]: '\n'.join([','.join(h) for h in zip(*df.columns)]) + '\n'
Out[21]: 'AA,BB,CC\nDD,EE,FF\n'