How to reshape numpy array in this way?

Question

I want to reshape a into b, how to quickly do it?

Basically, when reshaping the array, how to always use the first item in each group, then the second item, then the third one?

Input:

import numpy as np

# 3 repeats, each has 2 variables, each has 4 times
a=np.array([[['r1_v1_t1','r1_v1_t2','r1_v1_t3','r1_v1_t4'],
            ['r1_v2_t1','r1_v2_t2','r1_v2_t3','r1_v2_t4']],

[['r2_v1_t1','r2_v1_t2','r2_v1_t3','r2_v1_t4'],
            ['r2_v2_t1','r2_v2_t2','r2_v2_t3','r2_v2_t4']],

[['r3_v1_t1','r3_v1_t2','r3_v1_t3','r3_v1_t4'],
            ['r3_v2_t1','r3_v2_t2','r3_v2_t3','r3_v2_t4']]
            ])

# 4 times, each has 3 repeats, each has 2 variables
b=np.array([[['r1_v1_t1','r1_v2_t1'],['r2_v1_t1','r2_v2_t1'],['r3_v1_t1','r3_v2_t1']],
[['r1_v1_t2','r1_v2_t2'],['r2_v1_t2','r2_v2_t2'],['r3_v1_t2','r3_v2_t2']],
[['r1_v1_t3','r1_v2_t3'],['r2_v1_t3','r2_v2_t3'],['r3_v1_t3','r3_v2_t3']],
[['r1_v1_t4','r1_v2_t4'],['r2_v1_t4','r2_v2_t4'],['r3_v1_t4','r3_v2_t4']]])

# 4 times, each has 2 variables, each has 3 repeats
#print(a.T)

#print(np.reshape(a,(4,3,2), order='F')) not work
#print(np.reshape(a,(4,3,2))) not work

thank you! The transpose works! Sorry, I was actually trying to solve a more complex problem, so I re-edited the question now. — lanselibai
– lanselibai, Commented Mar 23, 2018 at 17:14

NickBraunagel · Accepted Answer · 2018-03-23 22:37:35Z

1

You can swap the array's axes so the shape of a matches the shape of b. Numpy's swapaxes can achieve this:

new_a = np.swapaxes( np.swapaxes(a,0,2) ,1,2)

You can test that this new_a is equivalent to b:

print (new_a == b).all()  # True

Here's a working gist.

answered Mar 23, 2018 at 22:37

NickBraunagel

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1 Comment

lanselibai Over a year ago

fantastic! so powerful!

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