Converting a List of Lists into a numpy array [duplicate]

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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
– user3483203, Commented Aug 14, 2018 at 14:30
Do you want it to be a numpy array with numpy arrays within it? — Hadus
– Hadus, Commented Aug 14, 2018 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
– Rohan Bhowmik, Commented Aug 14, 2018 at 14:33

Hadus · Accepted Answer · 2018-08-14 14:36:26Z

2

To create a list of numpy arrays:

np_arrays = []

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

answered Aug 14, 2018 at 14:36

Hadus

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Rohan Bhowmik · Accepted Answer · 2018-08-14 14:38:09Z

1

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)

answered Aug 14, 2018 at 14:38

Rohan Bhowmik

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