Python | Convert list of tuple into dictionary

• Last Updated : 26 Aug, 2019

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 initializationindices = ['x','y','z','w','t','r']relation =[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]  #dictionary initializationOutput = {}  #Iteration for elem in indices:     temp= []     for rel in relation:          if elem in rel:               if elem == rel:                    temp.append(rel)               else:                    temp.append(rel)            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.  #Importingimport networkx as nx   #List initializationindices = ['x','y','z','w','t','r']relation =[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]  #dictionary initializationOutput = {}  #Using networkx to solve temp=nx.Graph(relation)temp.add_nodes_from(indices)Output = nx.to_dict_of_lists(temp)  #Printingprint("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.  #Importingfrom itertools import groupbyfrom operator import itemgetter  #List initializationindices = ['x','y','z','w','t','r']relation =[('x', 'y'), ('x', 'z'), ('x', 'w'), ('y', 'z'), ('y', 'w'), ('z', 'w')]  #Using itertools.groupby and mapsedge = 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 listOutput = defaultdict(list, mapping)Output = dict(mapping)Output.update({vertex: [] for vertex in indices if vertex not in mapping})  #Printingprint("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']}

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