slicing a numpy array based on specific Boolean indices

Question

I have a numpy array ( X )

1   2   3   4
3   4   5   6
5   6   7   8

and a Booelan index array ( ind )

0 1 1 0

I would like to slice the numpy array based on the index. ie The resultant array after silicing should only have columns 2 and 3 (with corresponding index 1):

2   3   
4   5   
6   7   

I tried X[:,ind] , but it didn't work.

Answer 1

You need to convert ind to a boolean array . An easy way to do this is by using numpy.array() :

numpy.array(ind, dtype=bool)

You can then use X[:,ind]

Answer 2

You need to convert ind to dtype: bool .

This can be done by masking with ind == 1 .

That is to say,

>>> X[:,ind == 1]
array([[2, 3],
       [4, 5],
       [6, 7]])