Split a list with n*n elements into n lists with n elements in every list

Question

I am trying to come up with a function that takes an input x and split a big list with the number of elements x*x into x smaller lists with x elements in every list E.g:

big_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]

def split_list (x):
big_list = pairs (x)
small_list = [big_list[0:x] for x in range (x)]

My output has to be:

[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]

but I'm not getting it, what do you recommend ?

https://stackoverflow.com/questions/30379560/what-does-this-function-do-python-iterators — Josh Lee, Sep 29 '17 at 14:02
What would your expected output be if `big_list` had 15, or 17 elements? — Tom Dalton, Sep 29 '17 at 14:20

score 12 · Accepted Answer · edited Sep 29 '17 at 14:01

12

You can try this:

big_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]

def split_list (x):
   return [big_list[i:i+x] for i in range(0, len(big_list), x)]

print(split_list(4))

Output:

[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]

edited Sep 29 '17 at 14:01

Alan Kavanagh

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answered Sep 29 '17 at 13:58

Ajax1234

69,937
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score 5 · Answer 2 · answered Sep 29 '17 at 14:04

5

I use this code all the time.

def chunkify(items, chunk_len):
    return [items[i:i+chunk_len] for i in range(0,len(items),chunk_len)]

answered Sep 29 '17 at 14:04

Evan

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score 3 · Answer 3 · answered Sep 29 '17 at 14:09

Here's one solution:

def split_list(big_list, x):
    list_size = len(big_list)
    splits = int(list_size / x)

    return [big_list[k*x:k*x+x] for k in range(splits)]

big_list = [i+1 for i in range(16)]
print(big_list)
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]

small_list = split_list(big_list, 4)
print(small_list)
# [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]


small_list = split_list(big_list, 2)
print(small_list)
# [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12], [13, 14], [15, 16]]

small_list = split_list(big_list, 3)
print(small_list)
# [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12], [13, 14, 15]]

score 2 · Answer 4 · answered Sep 29 '17 at 14:00

First you want to get the size using square root, so you for a list of size n you would have an m x m matrix with m = n ** 0.5. Let's first define your function:

def square(array):
    n = len(array)
    m = int(n ** 0.5)

Since list sizes have to be integers, we have to call int on the result. Next, we want to start from 0 and count i up to n by m each time, taking m elements starting from i:

def square(array):
    n = len(array)
    m = int(n ** 0.5)
    result = []
    for i in range(0, n, m):
        result.append(array[i:i + m])
    return result

And that's it.

Alternatively, s=lambda a:(lambda m:[a[i*m:i*m+m]for i in range(m)])(int(len(a)**.5))

Dadep · Answer 5 · 2017-09-29T14:08:11.020

why not use numpy :

>>> import numpy as np
>>> big_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
>>> a=np.array(big_list)
>>> a
array([ 1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16])
>>> n=int(len(big_list)**0.5)
>>> a.reshape(n,n)
array([[ 1,  2,  3,  4],
       [ 5,  6,  7,  8],
       [ 9, 10, 11, 12],
       [13, 14, 15, 16]])

or just :

>>> big_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
>>> n=int(len(big_list)**0.5)
>>> new_list=[big_list[i:i+n] for i in range(0, len(big_list), n)]
>>> new_list
[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]

Split a list with n*n elements into n lists with n elements in every list

5 Answers5