Index duplicates in a multidimensional array

Question

Index only duplicates in a multidimensional array.

Example

a = [[279, 629, 590], [382, 825, 279], [629, 569, 113], [382, 785, 296]]

3D array with duplicates, I want to return the row and column of duplicates.

results = [[[279], [[0, 0], [1, 3]], [[629], [[0, 1], [2, 0]], [[382], [[1, 0], [3, 0]]]

I am looking to return only the duplicate elements along with the row and columns.

That's an interesting problem; how have you tried to solve it? — Scott Hunter
– Scott Hunter, Commented Mar 4, 2016 at 19:39
Is using Numpy an option? It would make things easier. (And technically, there are no arrays in the Python core language, let alone multi-dimensional arrays. There are lists of lists, but that's something different, and the difference matters in some cases.) — Sven Marnach
– Sven Marnach, Commented Mar 4, 2016 at 19:41
I really didn't know where to start with solving this problem. I like to provide attempts to this problem. — QuantumTraveler
– QuantumTraveler, Commented Mar 4, 2016 at 19:45
Welcome to StackOverflow. Please read and follow the posting guidelines in the help documentation. on topic and how to ask apply here. — Prune
– Prune, Commented Mar 4, 2016 at 19:45
I think I can use numpy to get the column and row length and then loop through the multidimensional array, adding found duplicates to a dictionary. — QuantumTraveler
– QuantumTraveler, Commented Mar 4, 2016 at 19:46

MSeifert · Accepted Answer · 2016-03-04 20:02:07Z

1

One possible solution for this problem is to get a dict (I used a defaultdict because it is nicer if one doesn't need to initiate empty lists by hand) where the key is the value and the value is a list of the coordinates for this value:

a = [[279, 629, 590], [382, 825, 279], [629, 569, 113], [382, 785, 296]]
from collections import defaultdict
elements = defaultdict(list)
for row_index in range(len(a)):
    for col_index in range(len(a[row_index])):
        elements[a[row_index][col_index]].append([row_index, col_index])

The next step would be to create a list of the value and the coordinates like you specified:

multiples = [[[i], elements[i]] for i in elements if len(elements[i]) > 1]

Which would be:

[[[629], [(0, 1), (2, 0)]],
 [[279], [(0, 0), (1, 2)]],
 [[382], [(1, 0), (3, 0)]]]

answered Mar 4, 2016 at 20:02

MSeifert

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