Proper way to create array/list of arrays from arrays/lists of elements in python

Question

Suppose I have numpy arrays or lists a and b with the same lengths, e.g. a = numpy.array([1,2,3]), b = numpy.array([4,5,6]) and I want to create a numpy.array or list of pairs of the form numpy.array([a[i],b[i]]). The following code in principle works:

P = [numpy.array([a[i],b[i]]) for i in range(len(a))]

However, I suspect that there is a more elegant way to do it. Moreover, the above code does not work in case a and b are scalars, rather than arrays. Ideally, I would like the code to be able to handle both cases. Any suggestions?

There is no built-in `array`; if you mean Numpy arrays then explicitly say and show that, similarly if you mean the standard library `array` module or anything else. — Karl Knechtel, Jan 23 '23 at 15:28
@MichaelButscher Thanks! It does not work if a and b are scalars, though, right? — Quercus Robur, Jan 23 '23 at 15:29
Cool, added a separate duplicate link for Numpy-specific approaches. — Karl Knechtel, Jan 23 '23 at 15:33

score 1 · Accepted Answer · answered Jan 23 '23 at 15:29

Assuming, numpy arrays:

P = list(np.c_[a, b])

Or:

P = list(np.vstack([a, b]).T)

Output:

[array([1, 4]), array([2, 5]), array([3, 6])]

NB. It's generally not a good idea to have lists of arrays, better keep the stacked array.

np.c_[a, b]

array([[1, 4],
       [2, 5],
       [3, 6]])

Reproducible input:

import numpy as np
a = np.array([1,2,3])
b = np.array([4,5,6])

Proper way to create array/list of arrays from arrays/lists of elements in python

1 Answers1