Python | Convert list of tuple into dictionary

Given a list containing all the element and second list of tuple depicting the relation between indices, the task is to output a dictionary showing the relation of every element from the first list to every other element in the list.
These type of problems are often encountered in Coding competition.
Below are some ways to achieve the above task.

Input:
indices = ['x','y','z','w','t','r']
relation =[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]
Output:
{'x': ['y', 'z', 'w'], 'y': ['x', 'z', 'w'], 'z': ['x', 'y', 'w'], 
'w': ['x', 'y', 'z'], 't': [], 'r': []}

Method #1: Using iteration is the easiest way to solve any task

#Python code to convert list of tuple into dictionary showing
#relation of every element from first list to every other element in the list.

#List initialization
indices = ['x','y','z','w','t','r']
relation =[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]

#dictionary initialization
Output = {}

#Iteration
for elem in indices:
     temp= []
     for rel in relation:
          if elem in rel:
               if elem == rel[0]:
                    temp.append(rel[1])
               else:
                    temp.append(rel[0])

     Output[elem] = temp
     temp = []

print("Initial list of tuple is :")
print(relation)
print("Converted dictionary of list :")
print(Output)

Output :
Initial list of tuple is :
[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]
Converted dictionary of list :
{'w': ['x', 'y', 'z'], 'r': [], 'x': ['y', 'z', 'w'], 't': [], 
'y': ['x', 'z', 'w'], 'z': ['x', 'y', 'w']}

Method #2: Using networkx is the most simplest and shortest
way to convert list of tuple into dictionary

#Python code to convert list of tuple into dictionary showing
#relation of every element from first list to every other element in the list.

#Importing
import networkx as nx

#List initialization
indices = ['x','y','z','w','t','r']
relation =[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]

#dictionary initialization
Output = {}

#Using networkx to solve
temp=nx.Graph(relation)
temp.add_nodes_from(indices)
Output = nx.to_dict_of_lists(temp)

#Printing
print("Initial list of tuple is :")
print(relation)
print("Converted dictionary of list :")
print(Output)

Output :
Initial list of tuple is :
[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]
Converted dictionary of list :
{'w': ['x', 'y', 'z'], 'r': [], 'x': ['y', 'z', 'w'], 't': [], 
'y': ['x', 'z', 'w'], 'z': ['x', 'y', 'w']}

Method #3: Using itertools and groupby is another way to convert list of tuple into dictionary.

#Python code to convert list of tuple into dictionary showing
#relation of every element from first list to every other element in the list.

#Importing
from itertools import groupby
from operator import itemgetter

#List initialization
indices = ['x','y','z','w','t','r']
relation =[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]

#Using itertools.groupby and maps
edge = relation + [tuple(reversed(pair)) for pair in relation]
st = itemgetter(0)
end = itemgetter(1)
groups = groupby(sorted(edge), key=st)
mapping = {vertex: list(map(end, edges)) for vertex, edges in groups}
from collections import defaultdict

#Output list
Output = defaultdict(list, mapping)
Output = dict(mapping)
Output.update({vertex: [] for vertex in indices if vertex not in mapping})

#Printing
print("Initial list of tuple is :")
print(relation)
print("Converted dictionary of list :")
print(Output)

Output :
Initial list of tuple is :
[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]
Converted dictionary of list :
{'w': ['x', 'y', 'z'], 'r': [], 'x': ['y', 'z', 'w'], 't': [], 
'y': ['x', 'z', 'w'], 'z': ['x', 'y', 'w']}