Index pandas DataFrame by column numbers, when column names are integers

Question

I am trying to keep just certain columns of a DataFrame, and it works fine when column names are strings:

In [2]: import numpy as np

In [3]: import pandas as pd         


        

Answer 1

This is certainly one of those things that feels like a bug but is really a design decision (I think).

A few work around options:

rename the columns with their positions as their name:

 df.columns = arange(0,len(df.columns))

Another way is to get names from df.columns:

print df[ df.columns[[1,3]] ]
   11  13
x   1   3
y   8  10
u  15  17
z  22  24
w  29  31

I suspect this is the most appealing as it just requires adding a wee bit of code and not changing any column names.

Answer 2

This is exactly the purpose of iloc, see here

In [37]: df
Out[37]: 
   10  11  12  13  14  15  16
x   0   1   2   3   4   5   6
y   7   8   9  10  11  12  13
u  14  15  16  17  18  19  20
z  21  22  23  24  25  26  27
w  28  29  30  31  32  33  34

In [38]: df.iloc[:,[1,3]]
Out[38]: 
   11  13
x   1   3
y   8  10
u  15  17
z  22  24
w  29  31

Answer 3

Just convert the headers from integer to string. This should be done almost always as a best practice when working with pandas datasets to avoid surprise

df.columns = df.columns.map(str)