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Python – Group records by Kth column in List

  • Last Updated : 09 Mar, 2020

Sometimes, while working with Python lists, we can have a problem in which we need to perform grouping of records on basis of certain parameters. One such parameters can be on the Kth element of Tuple. Lets discuss certain ways in which this task can be performed.

Method #1 : Using loop + defaultdict()
The combination of above methods can be used to perform this task. In this we store the tuples in different list on basis of Kth Column using defaultdict and iteration using loop.

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# Python3 code to demonstrate 
# Group records by Kth column in List
# using loop + defaultdict()
from collections import defaultdict
  
# Initializing list
test_list = [('Gfg', 1), ('is', 2), ('Gfg', 3), ('is', 4), ('best', 5)]
  
# printing original list
print("The original list is : " + str(test_list))
  
# Initializing K 
K = 0
  
# Group records by Kth column in List
# using loop + defaultdict()
temp = defaultdict(list)
for ele in test_list:
    temp[ele[K]].append(ele)
res = list(temp.values())
  
# printing result 
print ("The list after grouping : " + str(res))
Output :



The original list is : [('Gfg', 1), ('is', 2), ('Gfg', 3), ('is', 4), ('best', 5)]
The list after grouping : [[('Gfg', 1), ('Gfg', 3)], [('is', 2), ('is', 4)], [('best', 5)]]

 

Method #2 : Using itemgetter() + groupby() + list comprehension
The combination of above function can also be performed using above functions. In this, itemgetter is used to select Kth Column, groupby() is used to group and list comprehension is used to compile the result.




# Python3 code to demonstrate 
# Group records by Kth column in List
# using itemgetter() + list comprehension + groupby()
from operator import itemgetter
from itertools import groupby
  
# Initializing list
test_list = [('Gfg', 1), ('is', 2), ('Gfg', 3), ('is', 4), ('best', 5)]
  
# printing original list
print("The original list is : " + str(test_list))
  
# Initializing K 
K = 0
  
# Group records by Kth column in List
# using loop + defaultdict()
temp = itemgetter(K)
res = [list(val) for key, val in groupby(sorted(test_list, key = temp), temp)]
  
# printing result 
print ("The list after grouping : " + str(res))
Output :
The original list is : [('Gfg', 1), ('is', 2), ('Gfg', 3), ('is', 4), ('best', 5)]
The list after grouping : [[('Gfg', 1), ('Gfg', 3)], [('is', 2), ('is', 4)], [('best', 5)]]



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