How to create a numpy array of lists?

Question

I want to create a numpy array in which each element must be a list, so later I can append new elements to each.

I have looked on google and here on stack overflow a

Answer 1

Lists aren't very numpy anyway, so maybe a tuple of lists is good enough for you. You can get that easily and rather efficiently with an iterator expression:

fiveLists = tuple([] for _ in range(5))

You can leave out the tuple if you only need it once (gives you the raw iterator).

You can use this to create a numpy array if you really want to:

arrayOfLists = np.fromiter(([] for _ in range(5)), object)

Edit: as of July 2020, you get "ValueError: cannot create object arrays from iterator"