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Python | Sort a list according to the second element in sublist

  • Difficulty Level : Easy
  • Last Updated : 21 Nov, 2018

In this article, we will learn how to sort any list, according to the second element of the sublist present within the main list. We will see two methods of doing this. We will learn three methods of performing this sort. One by the use of Bubble Sort, second by using the sort() method and last but not the least by the use of sorted() method. In this program, we have sorted the list in ascending order.
Examples:

Input : [['rishav', 10], ['akash', 5], ['ram', 20], ['gaurav', 15]]
Output : [['akash', 5], ['rishav', 10], ['gaurav', 15], ['ram', 20]]

Input : [['452', 10], ['256', 5], ['100', 20], ['135', 15]]
Output : [['256', 5], ['452', 10], ['135', 15], ['100', 20]]

Method 1: Using the Bubble Sort technique
Here we have used the technique of Bubble Sort to perform the sorting. We have tried to access the second element of the sublists using the nested loops. This performs the in-place method of sorting. The time complexity is similar to the Bubble Sort i.e., O(n^2)




# Python code to sort the lists using the second element of sublists
# Inplace way to sort, use of third variable
def Sort(sub_li):
    l = len(sub_li)
    for i in range(0, l):
        for j in range(0, l-i-1):
            if (sub_li[j][1] > sub_li[j + 1][1]):
                tempo = sub_li[j]
                sub_li[j]= sub_li[j + 1]
                sub_li[j + 1]= tempo
    return sub_li
  
# Driver Code
sub_li =[['rishav', 10], ['akash', 5], ['ram', 20], ['gaurav', 15]]
print(Sort(sub_li))

Output:

[['akash', 5], ['rishav', 10], ['gaurav', 15], ['ram', 20]]

Method 2: Sorting by the use of sort() method
While sorting via this method the actual content of the tuple is changed, and just like the previous method, in-place method of sort is performed.






# Python code to sort the tuples using second element 
# of sublist Inplace way to sort using sort()
def Sort(sub_li):
  
    # reverse = None (Sorts in Ascending order)
    # key is set to sort using second element of 
    # sublist lambda has been used
    sub_li.sort(key = lambda x: x[1])
    return sub_li
  
# Driver Code
sub_li =[['rishav', 10], ['akash', 5], ['ram', 20], ['gaurav', 15]]
print(Sort(sub_li))

Output:

[['akash', 5], ['rishav', 10], ['gaurav', 15], ['ram', 20]]

Method 3: Sorting by the use of sorted() method
Sorted() sorts a list and always returns a list with the elements in a sorted manner, without modifying the original sequence. It takes three parameters from which two are optional, here we tried to use all of the three:

  1. Iterable : sequence (list, tuple, string) or collection (dictionary, set, frozenset) or any other iterator that needs to be sorted.
  2. Key(optional) : A function that would server as a key or a basis of sort comparison.
  3. Reverse(optional) : To sort this in ascending order we could have just ignored the third parameter, which we did in this program. If set true, then the iterable would be sorted in reverse (descending) order, by default it is set as false.




# Python code to sort the tuples using second element 
# of sublist Function to sort using sorted()
def Sort(sub_li):
  
    # reverse = None (Sorts in Ascending order)
    # key is set to sort using second element of 
    # sublist lambda has been used
    return(sorted(sub_li, key = lambda x: x[1]))    
  
# Driver Code
sub_li =[['rishav', 10], ['akash', 5], ['ram', 20], ['gaurav', 15]]
print(Sort(sub_li))

Output:

[['akash', 5], ['rishav', 10], ['gaurav', 15], ['ram', 20]]

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