Python | Update a list of tuples using another list

Last Updated : 11 Mar, 2019

Given two list of tuples, write a Python program to update ‘list1’ according to the ‘list2’ and return an updated list.

Examples:

Input : list1 = [('x', 0), ('y', 5)]
        list2 = [('x', 100), ('y', 200)]
Output : [('x', 100), ('y', 200)]

Input : list1 = [('a', 0), ('b', 0), ('c', 0)]
        list2 = [('a', 1), ('b', 2)]
Output :[('a', 1), ('b', 2), ('c', 0)]

Approach #1 Pythonic Naive
This is a Pythonic naive approach. We simply convert the list of tuples into a dictionary and just update it with list2 and convert the dictionary back to list.

# Python3 code to Update a list 
# of tuples according to another list
  
def merge(list1, list2): 
    dic = dict(list1)
    dic.update(dict(list2))
    return list(dic.items())
  
# Driver Code
list1 = [('a', 0), ('b', 0), ('c', 0)]
list2 = [('a', 5), ('c', 3)]
print(merge(list1, list2))

Output:

[('a', 5), ('b', 0), ('c', 3)]

Approach #2 Using defaultdict
Python collections module provides defaultdict() method which is used in this approach. First we initialize ‘dic’ with defaultdict method passing list as factory. Use a loop to append the left element of each tuple as key and right element of each tuple as value for both the lists. Now simply use the sorted function and produce the list in such a way that the for each unique key it keeps the maximum value of right element of tuple.

# Python3 code to Update a list 
# of tuples according to another list
  
from collections import defaultdict
  
def merge(list1, list2): 
    dic = defaultdict(list)
    for i, j in list1 + list2:
        dic[i].append(j)
          
    return sorted([(i, max(j)) for i, j in dic.items()],
    key = lambda x:x[0])
  
# Driver Code
list1 = [('a', 0), ('b', 0), ('c', 0)]
list2 = [('a', 5), ('c', 3)]
print(merge(list1, list2))

Output:

[('a', 5), ('b', 0), ('c', 3)]

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