When I have a=1
and b=2
, I can write a,b=b,a
so that a
and b
are interchanged with each other.
I use this matrix as an array:
[ 1, 2, 0, -2]
[ 0, 0, 1, 2]
[ 0, 0, 0, 0]
Swapping the columns of a numpy array does not work:
import numpy as np
x = np.array([[ 1, 2, 0, -2],
[ 0, 0, 1, 2],
[ 0, 0, 0, 0]])
x[:,1], x[:,2] = x[:,2], x[:,1]
It yields:
[ 1, 0, 0, -2]
[ 0, 1, 1, 2]
[ 0, 0, 0, 0]
So x[:,1]
has simply been overwritten and not transferred to x[:,2]
.
Why is this the case?
If you're trying to swap columns you can do it by
print x
x[:,[2,1]] = x[:,[1,2]]
print x
output
[[ 1 2 0 -2]
[ 0 0 1 2]
[ 0 0 0 0]]
[[ 1 0 2 -2]
[ 0 1 0 2]
[ 0 0 0 0]]
The swapping method you mentioned in the question seems to be working for single dimensional arrays and lists though,
x = np.array([1,2,0,-2])
print x
x[2], x[1] = x[1], x[2]
print x
output
[ 1 2 0 -2]
[ 1 0 2 -2]