How to Order a multidimensional List using another list

Question

Quick Summary:

need_to_reorder = [['a', 'b', 'c', 'd'], [1, 2, 3, 4]]

I want to set an order for the need_to_reorder[0][x] x values using my sorting array

sorting_array = [1, 3, 0, 2]

Required result: need_to_reorder will equal

[['b', 'd', 'a', 'c'], [2, 4, 1, 3]]

Searching for the answer, I tried using numPy:

import numpy as np
sorting_array = [1, 3, 0, 2]
i = np.array(sorting_array)
print i  ## Results: [1 3 0 2] <-- No Commas?
need_to_reorder[:,i]

RESULTS:

TypeError: list indicies must be integers, not tuple

I'm looking for a correction to the code above or an entirely different approach.

For input there is a csv file which is being read into a multidimensional array. Also, on input the client will give me instructions on how to reorder the data. There are some cleanup changes being made to some of the data. After the cleanup, I want to reorder the data and print the results. — Eric Hansen, May 20 '15 at 20:06

score 3 · Accepted Answer · edited May 23 '17 at 12:15

3

You can try a simple nested comprehension

>>> l = [['a', 'b', 'c', 'd'], [1, 2, 3, 4]]
>>> s = [1, 3, 0, 2]
>>> [[j[i] for i in s] for j in l]
[['b', 'd', 'a', 'c'], [2, 4, 1, 3]]

If you need this as a function you can have a very simple function as in

def reorder(need_to_reorder,sorting_array)
    return [[j[i] for i in sorting_array] for j in need_to_reorder]

Do note that this can be solved using map function also. However in this case, a list comp is preferred as the map variant would require a lambda function. The difference between map and a list-comp is discussed in full length in this answer

edited May 23 '17 at 12:15

Community

1
1

answered May 20 '15 at 20:08

Bhargav Rao

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yes, same as mine, but i think a dedicated function is more clear for something like this – Pete Cacioppi May 20 '15 at 20:13
@Pete ... `map` is a bit tedious here. I will add a few points as to why I chose a lisco over `map`. Dedicated funcs can be left to the OP. This is because he needs this as a plug-in. So we may as well wait for the OP to clarify – Bhargav Rao May 20 '15 at 20:15
I think in terms of maps and lambdas. I guess not everyone else does (sigh) – Pete Cacioppi May 20 '15 at 20:18
@Pete Do avoid a `lambda` whenever possible. – Bhargav Rao May 20 '15 at 20:20
@BhargavRao You forgot to put a function name. – Malik Brahimi May 20 '15 at 20:41

score 0 · Answer 2 · answered May 20 '15 at 20:10

0

def order_with_sort_array(arr, sort_arr):
    assert len(arr) == len(sort_arr)
    return [arr[i] for i in sort_arr]

sorting_array = [1, 3, 0, 2]
need_to_reorder = [['a', 'b', 'c', 'd'], [1, 2, 3, 4]]

after_reordered =  map(lambda arr : order_with_sort_array(arr, sorting_array), 
                      need_to_reorder)

answered May 20 '15 at 20:10

Pete Cacioppi

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I would have upvoted this answer if it wasn't a code block. It is a good answer, no doubt, but it needs some statements around it to. – Bhargav Rao May 20 '15 at 20:22
I would but don't have enough karma or whatever to do it. – Eric Hansen May 20 '15 at 21:19

score 0 · Answer 3 · answered May 20 '15 at 20:13

0

This should work

import numpy as np
ntr = np.array([['a', 'b', 'c', 'd'], [1, 2, 3, 4]])
sa = np.array([1, 3, 0, 2])
print np.array( [ntr[0,] , np.array([ntr[1,][sa[i]] for i in range(sa.shape[0])])] )
>> [['a' 'b' 'c' 'd'],['2' '4' '1' '3']]

answered May 20 '15 at 20:13

farhawa

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How to Order a multidimensional List using another list

3 Answers3