convert a list of lists to an array of list

Question

I am trying to convert a list into an array. The list is:

list = [[59.99, 58.648, 58.608, 62.944, 51.648, 49.397, 44.766, 40.066, 35.641, 33.825, 31.112, 28.644, 26.441, 24.592, 26.767], ... , [253.99, 7.8, 58.28, 744.4, 59.08, 10.37, 2.9, 33.356, 64.2, 4.5, 3.18, 24,77, 7.18, 92,5, 95.87]]

I have tried this :

A = numpy.array(list)

but when I type A, I get the following array:

array([list([59.99, 58.648, 58.608, 62.944, 51.648, 49.397, 44.766, 40.066, 35.641, 33.825, 31.112, 28.644, 26.441, 24.592, 26.767]), ..., list([253.99, 7.8, 58.28, 744.4, 59.08, 10.37, 2.9, 33.356, 64.2, 4.5, 3.18, 24,77, 7.18, 92,5, 95.87])], dtype=object)

How can I get ride of list() in the array ?

What do you see for set(map(len, L)) where L is your input list (don't shadow built-ins, i.e. call your input L not list)? If your sublists are not the same length, what you see is inevitable. — jpp
– jpp, Commented Aug 9, 2018 at 14:09
That is a 1d array containing lists. Given the mix of list sizes it can't create a 2d array. — hpaulj
– hpaulj, Commented Aug 9, 2018 at 14:15
yes my sublists are not the same length. Maybe I have to extract each list and zero-pad it so that I can convert the whole list to an array — A. Arfaoui
– A. Arfaoui, Commented Aug 9, 2018 at 14:16
It's just that I want to feed the whole thing to a neural net and I doesn't make any sense to say that a sample " s " has a feature " f " when it doesn't — A. Arfaoui
– A. Arfaoui, Commented Aug 9, 2018 at 14:19

jpp · Accepted Answer · 2018-08-09 14:32:05Z

1

You have sublists with mismatched lengths. As such, an array of lists is inevitable. As you suggested, you can zero-pad your sublists.

Here's one solution via a list comprehension:

L = [[0, 1], [2, 3, 4], [5, 6], [7]]

n = max(map(len, L))

res = np.array([i + [0]*(n-len(i)) for i in L])

print(res)

array([[0, 1, 0],
       [2, 3, 4],
       [5, 6, 0],
       [7, 0, 0]])

edited Aug 9, 2018 at 14:32

answered Aug 9, 2018 at 14:21

jpp

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1 Comment

A. Arfaoui Over a year ago

well it's working. I am afraid I connot escape the zero padding. Thank you.

Mohit Solanki · Accepted Answer · 2018-08-09 14:17:50Z

1

This should work

from itertools import chain

A = numpy.array(list(chain(*your_list)))

and don't name your variable list it is a reserved keyword

answered Aug 9, 2018 at 14:17

Mohit Solanki

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Comments

Matina G · Accepted Answer · 2018-08-09 14:21:27Z

1

Your list does not contain lists of equal length, and that is the reason why numpy is unable to convert directly. For instance, if you try :

mylist = [[1,2,3], [2,3,4]]
l = np.asarray(mylist)

This will work as expencted, since lists contained in mylist are of the same length. Still, you can try doing it in two steps:

mylist = [[59.99, 58.648, 58.608, 62.944, 51.648, 49.397, 44.766, 40.066, 35.641, 33.825, 31.112, 28.644, 26.441, 24.592, 26.767],[253.99, 7.8, 58.28, 744.4, 59.08, 10.37, 2.9, 33.356, 64.2, 4.5, 3.18, 24,77, 7.18, 92,5, 95.87]]
list_of_arr = [np.array(x) for x in mylist]
arr = np.array(arr)

so as to have arrays instead of lists to deal with

edited Aug 9, 2018 at 14:21

answered Aug 9, 2018 at 14:15

Matina G

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Comments

GeorgeLPerkins · Accepted Answer · 2018-08-09 14:37:21Z

0

First, don't use list as your variable name. list is a python reserved keyword. Use mylist or something else.

One thing you can do is create an empty list: compiledlist.

Then loop over the different arrays in mylist and extend them to compiledlist.

compiledlist = []
for sublist in mylist:
    compiledlist.extend(sublist)

A = np.array(compiledlist)

edited Aug 9, 2018 at 14:37

answered Aug 9, 2018 at 14:26

GeorgeLPerkins

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