CODEWITHSUNDEEP
pythonarrayssortingnumpy
Larisa
Larisa

Reputation: 791

Sorting numpy lists

I am having troubles working with NumPy arrays as I am new to NumPy. I have a big input which I read with sys.stdin, which is consisted of lines with 2 values and a space between them, representing a point or two coordinates. I then save it in a list which looks something like this:

np.array([[1, 3], [5, 6], [7, 2], [9, 9]])

I want to sort the list by their sums and then by their x-coordinate, but I am not sure how to do this.

I am also not sure how would I add that sum as the third element of each sublist, in case I wanted to add it.

Upvotes: 2

Views: 120

Answers (1)

karlson
karlson

Reputation: 5433

Relying on python's built-in sorted is inefficient for numpy-arrays, especially when these are big. Try this instead:

import numpy as np

l = np.array([[1, 3], [5, 6], [7, 2], [9, 9]])

ind = np.lexsort((l[:,0], l.sum(axis=1)))

sorted_l = l[ind]

ind will contain the indices of your original array, sorted by the two arrays given to lexsort. The last array is the primary sort column for lexsort. l[ind] selects these indices from your original array.

Upvotes: 3

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