CODEWITHSUNDEEP
pythonarraysnumpy
Zoojay
Zoojay

Reputation: 143

Tile and Modify a Numpy Array at the same time

Suppose I have a Numpy array like so: 

[10, 11, 12]

I want to copy it several times to form a new array, but subtract every element by 1 each time I copy, to produce: 

[[10 11 12]
 [ 9 10 11]
 [ 8  9 10]
 [ 7  8  9]
 [ 6  7  8]
 [ 5  6  7]]

This is simple with a list comprehension: 

import numpy as np
cycles = 6
a = np.array([10, 11, 12])

a = np.stack([a - i for i in range(cycles)])

However, I was wondering if there's a Numpy command that does this, or a more efficient way that doesn't use a list comprehension. I'm using Python 2.7.

Upvotes: 2

Views: 106

Answers (1)

Divakar
Divakar

Reputation: 221564

One approach would be with broadcasting -

a - np.arange(6)[:,None]

Sample run -

In [94]: a
Out[94]: array([10, 11, 12])

In [95]: a - np.arange(6)[:,None]
Out[95]: 
array([[10, 11, 12],
       [ 9, 10, 11],
       [ 8,  9, 10],
       [ 7,  8,  9],
       [ 6,  7,  8],
       [ 5,  6,  7]])

Upvotes: 4

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