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How do I create an array of matrices in python?

How do I create an array of matrices in python?

In MATLAB, I do something like this:

for i = 1:n
    a{i} = f(i)
end

where f(i)

is a function that returns a random, fixed-size matrix.

In python, I am working with numpy, but I don't understand how to do it.

import numpy as np
a = np.array([])
for i in range(0, n):
   # a.insert(i, f(i)) and does not work
   # a[i] = f(i)  and does not work
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2 answers


  • If you want a rank 3 Num-3 array and you know the shape ahead of time f(i)

    , you can preallocate the array:

    a = np.zeros((n,) + shape)
for i in range(n):
    a[i] = f(i)

  • If you only want a list (not a Numpy array) of matrices, use a list comprehension:

    a = [f(i) for i in range(n)]

  • Another way to get a Numpy array is to convert from the list comprehension above:

    a = np.array([f(i) for i in range(n)])

    However, this will be less efficient than # 1, because the results are f(i)

    first buffered in a dynamically sized list before the Numpy array is created.



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The best equivalent of a matrix cell array here is a list in python:



a = []
for i in range(n):
    a.append(f(i))
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