Supposed that I have an array like matrix using numpy like this.
import numpy as np
a = np.array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16], [17, 18, 19, 20]])
I want to change the [13, 14, 15, 16] into the first position so it will become something like this
array([[ 13, 14, 15, 16],
[ 1, 2, 3, 4 ],
[ 5, 6, 7, 8 ],
[ 9, 10, 11, 12 ],
[ 17, 18, 19, 20])
how can I do it? thanks
You can re-arrange the array with the row indices:
import numpy as np
a = np.array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16], [17, 18, 19, 20]])
b = a[[3,0,1,2,4],:]
print(b)
The output is:
[[13 14 15 16]
[ 1 2 3 4]
[ 5 6 7 8]
[ 9 10 11 12]
[17 18 19 20]]
Use np.delete and np.concatenate:
b = np.concatenate([a[[-2]], np.delete(a, -2, axis=0)])
print(b)
# Output
[[13 14 15 16]
[ 1 2 3 4]
[ 5 6 7 8]
[ 9 10 11 12]
[17 18 19 20]]
