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

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遥遥无期
遥遥无期 2021-02-20 00:14

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         


        
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  • 2021-02-20 00:40

    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.

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  • 2021-02-20 00:42

    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
    
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  • 2021-02-20 00:49

    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)
    
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