Variable length list to Numpy array

Suppose you have a variable length list and you want to convert it to a numb array

alist = [[1,2,3],[5,6]]

What is the efficient way to convert this list to a numpy array?

My first answer was using pandas and this is what I did?

import pandas as pd
data = pd.Dataframe(alist).fillna(0).values

This worked and I moved on to my other problem, but then realised if there is any other way which is more efficient. Turns out there is.

import itertools
data=np.array(list(itertools.izip_longest(*alist, fillvalue=0))).T

In python 2.7 and the following in python3

import itertools
data=np.array(list(itertools.zip_longest(*alist, fillvalue=0))).T

How Fast and efficient? See the below image.


Post writing the above I googled and found this link. Here is the result of both of the methods on the example data in the link.




Clearly, itertools is the winner.


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