Converting a List of Lists into a numpy array

Question

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I have a list of lists that looks something like...

>>> print(list_of_lists)
[[3, 3, 7, 8, 5], [9, 3, 3, 3, 3], [9, 10, 11, 3, 23, 3, 3], [20, 3, 3, 3, 3, 3, 3, 3], [20, 3, 3, 3, 3, 3, 3]]

I want to convert this list of lists into an array. However, when I do:

potential_numpy_array = numpy.array(list_of_lists)

or:

potential_numpy_array = numpy.asarray(list_of_lists)

I get something stranger:

>>> print(potential_numpy_array)
[list([3, 3, 17, 18, 16]) list([20, 3, 3, 3, 3]) list([20, 5, 6, 3, 12, 3, 3]) list([9, 3, 3, 3, 3, 3, 3, 3]) list([9, 3, 3, 3, 3, 3, 3])]

I've looked at many other questions but did not find an answer that could solve this problem.

Could someone please help me identify the source of confusion?

Thanks!

Don't use numpy with jagged lists, it will only cause you more of a headache later — user3483203, Aug 14 '18 at 14:30
Do you want it to be a numpy array with numpy arrays within it? — Hadus, Aug 14 '18 at 14:32
Check here: https://stackoverflow.com/questions/10346336/list-of-lists-into-numpy-array/26224619#26224619 — gizq, Aug 14 '18 at 14:32
@Hadus A list of numpy arrays is what I want (although a numpy array of numpy arrays would be fine too) — Rohan Bhowmik, Aug 14 '18 at 14:33
This is still a duplicate, there are many answers about making a 2d array of jagged list. — anishtain4, Aug 14 '18 at 14:45

score 2 · Accepted Answer · answered Aug 14 '18 at 14:36

2

To create a list of numpy arrays:

np_arrays = []

for array in arrays:
    np_arrays.append(numpy.array(array))

answered Aug 14 '18 at 14:36

Hadus

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score 1 · Answer 2 · answered Aug 14 '18 at 14:38

Thanks to the help of fellow stackOverflow users, I realized the list was "jagged" and needed to be padded. An example of a jagged list is:

[ [1,2],
  [1,3,2],
  [1] ]

I needed:

[ [1,2,0],
  [1,3,2],
  [1,0,0] ]

Since I am using TensorFlow and keras, I can just do:

test_data = keras.preprocessing.sequence.pad_sequences(test_data,
                                                    value=word_index["<PAD>"],
                                                    padding='post',
                                                    maxlen=12)

Converting a List of Lists into a numpy array

2 Answers2