Using Python to find matching arrays and combining into one array

Question

I would like to use Python to find the matching arrays such as [4012630, 0.07575758] and [4012630, 0.5671642]. Then I would like to combine them into 1 array and add the decimals. So it would become [4012630, 0.64292178].

Goal is to convert this array:

[[4012630, 0.07575758], 
[4012618, 0.014925373], 
[4012630, 0.5671642], 
[4012624, 0.029850746], 
[4012628, 0.41791046], 
[4012624, 0.07462686], 
[4012628, 0.04477612], 
[4012636, 0.2820513]]

Into this array:

[[4012630, 0.64292178],
[4012618, 0.014925373],
[4012624, 0.104477606],
[4012628, 0.46268658,
[4012636, 0.2820513]]

Possible duplicate of [How to make a set of lists](https://stackoverflow.com/questions/26783326/how-to-make-a-set-of-lists) — Simas Joneliunas, Nov 20 '19 at 06:51
using groupby and apply method to sum the values could also be an option https://stackoverflow.com/questions/39922986/pandas-group-by-and-sum — aayush_malik, Nov 20 '19 at 06:52

score 1 · Answer 1 · answered Nov 20 '19 at 09:27

There are many ways to solve this problem, here is my O(n) Time complexity solution :

def unique_sum(input_list):
  index_mapping = {}
  final_list = []
  for i in range(0, len(input_list)):
    if input_list[i][0] in index_mapping: 
      index = index_mapping[input_list[i][0]]
      final_list[index][1] += input_list[i][1]
    else:
      index_mapping[input_list[i][0]] = len(final_list)
      final_list.append([input_list[i][0], input_list[i][1]])
  return final_list

then you can call this function like :

data = [[4012630, 0.07575758], 
[4012618, 0.014925373], 
[4012630, 0.5671642], 
[4012624, 0.029850746], 
[4012628, 0.41791046], 
[4012624, 0.07462686], 
[4012628, 0.04477612], 
[4012636, 0.2820513]]


print(unique_sum(data))

score 0 · Answer 2 · answered Nov 20 '19 at 07:16

I propose the following solution. First, find out the unique labels. Then create the result list and initialize the sum to be 0. Then, iterate every element in the input list and add the value to the corresponding bin.

lst = [[4012630, 0.07575758],
[4012618, 0.014925373],
[4012630, 0.5671642],
[4012624, 0.029850746],
[4012628, 0.41791046],
[4012624, 0.07462686],
[4012628, 0.04477612],
[4012636, 0.2820513]]

def sumlist(lst):
    unique = list(set([x[0] for x in lst]))
    result = [[x,0] for x in unique]
    for i, value in lst:
        ind = unique.index(i)
        result[ind][1] += value
    return result

Thank you! Really simple solution and I was able to completely understand it! — Karem Darwich, Nov 20 '19 at 18:03

score 0 · Answer 3 · answered Apr 18 '20 at 22:20

You can use the Dictionary Data Structure for the following task.

Here's how I used it-

data = [[4012630, 0.07575758],
[4012618, 0.014925373],
[4012630, 0.5671642],
[4012624, 0.029850746],
[4012628, 0.41791046],
[4012624, 0.07462686],
[4012628, 0.04477612],
[4012636, 0.2820513]]

dict={}    #Declaring an empty dictionary.
for nat,dec in data:
    if nat not in dict:
        dic[nat]=dec
    else:
        dic[nat]+=dec
print(dict)

The output of the code is-

{4012630: 0.64292178, 
4012618: 0.014925373, 
4012624: 0.104477606, 
4012628: 0.46268657999999996, 
4012636: 0.2820513}

The only catch here is that the output will be a Dictionary instead of an array/list. But you can easily convert the dictionary into an array if required.

Khachatur Sarkisyan · Answer 4 · 2019-11-20T08:30:20.850

-1

from collections import defaultdict
def sum_func(l:list):
    temp1 = defaultdict(list)
    result = []
    for el in l:
        temp1[el[0]].append(el[1])
    for k, v in temp1.items():
        result.append([k, sum(v)])
    return result

edited Nov 20 '19 at 08:30

answered Nov 20 '19 at 07:18

Khachatur Sarkisyan

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Using Python to find matching arrays and combining into one array

4 Answers4