Python | Group tuple into list based on value

Last Updated : 11 Nov, 2019

Sometimes, while working with Python tuples, we can have a problem in which we need to group tuple elements to nested list on basis of values alloted to it. This can be useful in many grouping applications. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using itemgetter() + list comprehension + groupby()

The combination of above functions can be used to perform this task. In this, we access the value using itemgetter() and logic for grouping is performed using groupby() and list comprehension.

# Python3 code to demonstrate working of
# Group tuple into list based on value
# using itemgetter() + list comprehension + groupby()
from operator import itemgetter
from itertools import groupby
  
# initialize list 
test_list = [(1, 4), (2, 4), (6, 7), (5, 1), (6, 1), (8, 1)]
  
# printing original list 
print("The original list : " + str(test_list))
  
# Group tuple into list based on value
# using itemgetter() + list comprehension + groupby()
res = [[i for i, j in temp]\
      for key, temp in groupby(test_list, key = itemgetter(1))]
  
# printing result
print("The list after grouping by value : " + str(res))

Output :

The original list : [(1, 4), (2, 4), (6, 7), (5, 1), (6, 1), (8, 1)]
The list after grouping by value : [[1, 2], [6], [5, 6, 8]]

Method #2 : Using map() + itemgetter() + groupby() + list comprehension

This method is similar to the above method, the only difference is that we chose map for formation of keys as nested list for formation of new resultant lists.

# Python3 code to demonstrate working of
# Group tuple into list based on value
# using map() + itemgetter() + groupby() + list comprehension
from operator import itemgetter
from itertools import groupby
  
# initialize list 
test_list = [(1, 4), (2, 4), (6, 7), (5, 1), (6, 1), (8, 1)]
  
# printing original list 
print("The original list : " + str(test_list))
  
# Group tuple into list based on value
# using map() + itemgetter() + groupby() + list comprehension
res = [list(map(itemgetter(0), temp)) 
      for (key, temp) in groupby(test_list, itemgetter(1))]
  
# printing result
print("The list after grouping by value : " + str(res))

Output :

The original list : [(1, 4), (2, 4), (6, 7), (5, 1), (6, 1), (8, 1)]
The list after grouping by value : [[1, 2], [6], [5, 6, 8]]

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Python | Group tuple into list based on value