Index pandas DataFrame by column numbers, when column names are integers
pandas, python
Solution
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
Problem
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 In [4]: a = np.arange(35).reshape(5,7) In [5]: df = pd.DataFrame(a, ['x', 'y', 'u', 'z', 'w'], ['a', 'b', 'c', 'd', 'e', 'f', 'g']) In [6]: df Out[6]: a b c d e f g 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 [5 rows x 7 columns] In [7]: df[[1,3]] #No problem Out[7]: b d x 1 3 y 8 10 u 15 17 z 22 24 w 29 31 ``` However, when column names are integers, I am getting a key error: ``` In [8]: df = pd.DataFrame(a, ['x', 'y', 'u', 'z', 'w'], range(10, 17)) In [9]: df Out[9]: 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 [5 rows x 7 columns] In [10]: df[[1,3]] ``` Results in: ``` KeyError: '[1 3] not in index' ``` I can see why pandas does not allow that -> to avoid mix up between indexing by column names and column numbers. However, is there a way to tell pandas that I want to index by column numbers? Of course, one solution is to convert column names to strings, but I am wondering if there is a better solution.