How to make a numpy array with a dictionary's values?

Question

If I have a dictionary that looks like this:

sam = {1:np.array([1,2,3,4]), 2:np.array([2,4,6,8]) }

How can I make a numpy array with the dictionary values like this?

arr = ([[1,2,3,4], 
        [2,4,6,8]])

I thought np.fromiter(sam.values(), dtype=np.int16) might work, but it doesn't work probably because of its dtype.

Are the any functions to do this, instead of using for or any loops?

Answer 1

You could stack the values of your dictionary like this:

arr = np.stack(sam.values())

>>> arr
array([[1, 2, 3, 4],
       [2, 4, 6, 8]])

Answer 2

Dictionaries aren't considered ordered unless you are using Python 3.7+. So this is messy, but possible. The idea is to sort dict.items by key to give a list of tuples, then extract values.

from operator import itemgetter as iget

res = np.array(list(map(iget(1), sorted(sam.items(), key=iget(0)))))

array([[1, 2, 3, 4],
       [2, 4, 6, 8]])