Create variable padding around 1d numpy array

Question

arr= [1,2,3,4]
k = 4 (can be different)

so result will be 2 d array. How to do this without using any loop? and can't hard code k. k and arr can vary as per input. Must use numpy.pad

[[1,2,3,4,0,0,0], #k-1 zeros
 [0,1,2,3,4,0,0],
 [0,0,1,2,3,4,0],
 [0,0,0,1,2,3,4]]

2 revs · Accepted Answer · 2021-09-16 13:47:20Z

2

If you really have to do it without a loop (for educational purposes)

np.pad(np.tile(arr,[k,1]), [(0,0),(0,k)]).reshape(-1)[:-k].reshape(k,-1)

edited Sep 16, 2021 at 13:47

community wiki

2 revs
Michael Szczesny

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Comments

Osamoele · Accepted Answer · 2021-09-16 13:14:24Z

1

Using list comprehension as a one liner :

import numpy as np

arr= np.array([1,2,3,4])
k = 4

print( np.array( [ np.pad(arr, (0+i , k-1-i ) ) for i in range(0,k)] ) )

Out :

[[1 2 3 4 0 0 0]
 [0 1 2 3 4 0 0]
 [0 0 1 2 3 4 0]
 [0 0 0 1 2 3 4]]

edited Sep 16, 2021 at 13:14

answered Sep 16, 2021 at 13:07

Osamoele

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3 Comments

HelloGR Over a year ago

In real world your answer would have been perfect. But the question is no for or while loops or even list comprehension. Hidden loops are ok . @Osamoele

Osamoele Over a year ago

@Grafins Is there a reason you would refuse to work with any loop ? If it is for speed, you should consider making a dedicated function in cython, using foor loop as you wish there, and it will be faster than in python. At least not slower than the numpy C-implemented functions, that use SIMD and loops internally. Else, i see no real valid reason except for entertainment purposes but should be your challenge in that case ;)

HelloGR Over a year ago

its part of my programming assignment. So no loops. please understand

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