Python | Group tuples in list with same first value

Last Updated : 08 Apr, 2019

Given a list of tuples, the task is to print another list containing tuple of same first element. Below are some ways to achieve above tasks.

Example:

Input : [('x', 'y'), ('x', 'z'), ('w', 't')]

Output: [('w', 't'), ('x', 'y', 'z')]

Method #1: Using extend

# Python code to find common 
# first element in list of tuple
  
# Function to solve the task
def find(Input):
    out = {}
    for elem in Input:
        try:
            out[elem[0]].extend(elem[1:])
        except KeyError:
            out[elem[0]] = list(elem)
    return [tuple(values) for values in out.values()]
  
# List initialization
Input = [('x', 'y'), ('x', 'z'), ('w', 't')]
  
# Calling function
Output = (find(Input))
  
# Printing
print("Initial list of tuple is :", Input)
print("List showing common first element", Output)

Output:

Initial list of tuple is : [('x', 'y'), ('x', 'z'), ('w', 't')]
List showing common first element [('w', 't'), ('x', 'y', 'z')]

Method #2: Using defaultdict

# Python code to find common first
# element in list of tuple
  
# Importing
from collections import defaultdict
  
# Function to solve the task
def find(pairs):
    mapp = defaultdict(list)
    for x, y in pairs:
        mapp[x].append(y)
    return [(x, *y) for x, y in mapp.items()]
  
# Input list initialization
Input = [('p', 'q'), ('p', 'r'),
         ('p', 's'), ('m', 't')]
  
# calling function
Output = find(Input)
  
# Printing
print("Initial list of tuple is :", Input)
print("List showing common first element", Output)

Output:

Initial list of tuple is : [('p', 'q'), ('p', 'r'), ('p', 's'), ('m', 't')]
List showing common first element [('m', 't'), ('p', 'q', 'r', 's')]

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