CODEWITHSUNDEEP
pythonarraysnumpy
IanOverflow
IanOverflow

Reputation: 11

Is there a good way to 'flip' a list/matrix of numbers around some non-zero value?

I would like to 'flip' the values in a matrix, similar to numpy.absolute(), but flipping around the average value in the matrix; sort of like a fold.

The code below works, but I'd ideally like something that's more pythonic / faster. For my purposes, my array is 360x360, and this 'flipping' needs to be done many, many times, so running a 'for' loop through each and every element in the array seems like a bad idea. 

import numpy as np
arr = np.array([0,1,2,3,4])
avg = np.average(arr)
for i in range(len(arr)):
    x = arr[i]
    if x < avg:
        arr[i] = x + avg
print(arr)
>>> [2,3,2,3,4]

Thanks!

Upvotes: 1

Views: 71

Answers (1)

shx2
shx2

Reputation: 64318

This is the numpy way:

arr[arr < avg] += avg

The expression arr < avg creates a mask for selecting the elements in arr which are less than avg.

arr[...] selects those elements in arr.

+= avg increments them.

Upvotes: 2

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