How to Iterate over a list of numpy arrays in Python 3

Question

I currently have a list of numpy arrays. These arrays contain sets of 2D points. I'd like to iterate over each array in this list as depending on the contents of the array two scenarios can occur. The issue I'm running into is that when I try to iterate over the list like so:

for array in list:

it iterates over entries in the arrays as opposed to iterating over the arrays themselves. For example:

a = [array([[[1, 2]], [[3, 4]]], dtype=int32), array([[[5, 6]], [[7, 8)]]], dtype=int32)]
for array in a:
   print(array)

yields

when I'm expecting to get

[[1, 2], [3, 4]]
[[5, 6], [7, 8]]

Sorry, I'm unable to reproduce. Here's my code and I'm getting the output you expect. import numpy as np a = [np.array([[[1, 2]], [[3, 4]]], dtype=np.int32), np.array([[[5, 6]], [[7, 8]]], dtype=np.int32)] for i in a: print(i) [[[1 2]] [[3 4]]] [[[5 6]] [[7 8]]] — DrRobotNinja
– DrRobotNinja, Commented Apr 14, 2021 at 20:29
After fixing the syntax error in the example you gave, I cannot reproduce what you describe. — Karl Knechtel
– Karl Knechtel, Commented Apr 14, 2021 at 20:29
As a side note, please don't import names from np, especially if you're going to want to use them for other variables. Writing for array in a: in your sample makes array stop referring to the Numpy type and will mess up subsequent code. — Karl Knechtel
– Karl Knechtel, Commented Apr 14, 2021 at 20:31

Unmitigated · Accepted Answer · 2021-04-14 20:29:51Z

2

You can use numpy.squeeze to remove one dimension and use .tolist() to print in the format you want.

a = [array([[[1, 2]], [[3, 4]]], dtype=int32),array([[[5, 6]], [[7, 8]]], dtype=int32)]
for array in a:
  print(squeeze(array).tolist())

answered Apr 14, 2021 at 20:29

Unmitigated

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Comments

Mainly Karma · Accepted Answer · 2021-04-14 20:36:14Z

0

I think you have one too many brackets on each array as needed for your results

a = [array([[1, 2], [3, 4]], dtype=int32), array([[5, 6], [7, 8]], dtype=int32)]
for array in a:
   print(squeeze(array).tolist())

still produces

[[1, 2], [3, 4]]
[[5, 6], [7, 8]]

answered Apr 14, 2021 at 20:36

Mainly Karma

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