Python adding to dictionary only by key












0















Let's say i have a city (value) and people (key).
1 city can have many people.



(For example.):
Code:



cities = {'Berlin':{'Dan', 'john'},'Tokyo':{'John'}}

city_dict = {}

people = {}

for city in cities:

   ?


i want to construct a dictionary in python which insert only if a match between keys occurring.



(For example the desired result.):



{'dan' : {'dan':'berlin','dan':'colorado'},'john' : {'john':'berlin','john':'Tokyo'}}


Thanks.






python dictionary







share|improve this question




















  • 1





    What about {'dan' : {'berlin', 'colorado'},'john' : {'berlin', 'Tokyo'}} ? Why do you need the names again and again anyway?

    – Ayxan
    Dec 31 '18 at 11:38
















0















Let's say i have a city (value) and people (key).
1 city can have many people.



(For example.):
Code:



cities = {'Berlin':{'Dan', 'john'},'Tokyo':{'John'}}

city_dict = {}

people = {}

for city in cities:

   ?


i want to construct a dictionary in python which insert only if a match between keys occurring.



(For example the desired result.):



{'dan' : {'dan':'berlin','dan':'colorado'},'john' : {'john':'berlin','john':'Tokyo'}}


Thanks.






python dictionary







share|improve this question




















  • 1





    What about {'dan' : {'berlin', 'colorado'},'john' : {'berlin', 'Tokyo'}} ? Why do you need the names again and again anyway?

    – Ayxan
    Dec 31 '18 at 11:38














0












0








0


0






Let's say i have a city (value) and people (key).
1 city can have many people.



(For example.):
Code:



cities = {'Berlin':{'Dan', 'john'},'Tokyo':{'John'}}

city_dict = {}

people = {}

for city in cities:

   ?


i want to construct a dictionary in python which insert only if a match between keys occurring.



(For example the desired result.):



{'dan' : {'dan':'berlin','dan':'colorado'},'john' : {'john':'berlin','john':'Tokyo'}}


Thanks.






python dictionary







share|improve this question
















Let's say i have a city (value) and people (key).
1 city can have many people.



(For example.):
Code:



cities = {'Berlin':{'Dan', 'john'},'Tokyo':{'John'}}

city_dict = {}

people = {}

for city in cities:

   ?


i want to construct a dictionary in python which insert only if a match between keys occurring.



(For example the desired result.):



{'dan' : {'dan':'berlin','dan':'colorado'},'john' : {'john':'berlin','john':'Tokyo'}}


Thanks.






python dictionary




python dictionary






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Dec 31 '18 at 11:32









DeepSpace

38.5k44470




38.5k44470










asked Dec 31 '18 at 11:31









MoZZMoZZ

396




396








  • 1





    What about {'dan' : {'berlin', 'colorado'},'john' : {'berlin', 'Tokyo'}} ? Why do you need the names again and again anyway?

    – Ayxan
    Dec 31 '18 at 11:38














  • 1





    What about {'dan' : {'berlin', 'colorado'},'john' : {'berlin', 'Tokyo'}} ? Why do you need the names again and again anyway?

    – Ayxan
    Dec 31 '18 at 11:38








1




1





What about {'dan' : {'berlin', 'colorado'},'john' : {'berlin', 'Tokyo'}} ? Why do you need the names again and again anyway?

– Ayxan
Dec 31 '18 at 11:38





What about {'dan' : {'berlin', 'colorado'},'john' : {'berlin', 'Tokyo'}} ? Why do you need the names again and again anyway?

– Ayxan
Dec 31 '18 at 11:38












3 Answers
3






active

oldest

votes


















3














The desired result can't be achieved as dictionaries, by definition, can't contain duplicated keys.



You can, however, do the following (which is somehow close to the output you wanted):



from collections import defaultdict



cities = {'Berlin': {'Dan', 'John'}, 'Tokyo': {'John'}}

output = defaultdict(set)



for city, names in cities.items():

    for name in names:

        output[name].add(city)

print(output)

# defaultdict(<class 'set'>, {'Dan': {'Berlin'}, 'John': {'Berlin', 'Tokyo'}})





share|improve this answer































    2














    Other option, without dependencies and returning list of cities:



    cities = {'Berlin':{'Dan', 'John'},'Tokyo':{'John', 'Paul'}, 'Liverpool':{'John', 'Paul', 'George', 'Ringo'}, 'Colorado':{'Ringo'} }
    

    
res = {}
    
for k, v in cities.items():
    
  for e in v:
    
    res.setdefault(e,).append(k)
    

    
print(res)
    
#=> {'Dan': ['Berlin'], 'John': ['Berlin', 'Tokyo', 'Liverpool'], 'Paul': ['Tokyo', 'Liverpool'], 'Ringo': ['Liverpool', 'Colorado'], 'George': ['Liverpool']}





    share|improve this answer































      1














      You can't have a dictionary with duplicate keys like @DeepSpace indicated, so for your problem I can suggest you the following alternative.
      Use a dictionary with people's name for keys and for value the cities. And so when you want when combine the two for creating a list tuples or so on.



      people = {"Dan": ["Berlin","San Francisco"], "Mario": ["Rome"]}
      

      
for name, locations in people:
      
  #combine name with single city if needed
      
  for city in locations:
      
    tuple_tmp = (name,city)
      
    #next store it, print it,...


      This approach cons are:




      • You need to process the values

      • If you have city and and want to retrieve all names in this one is very slow operation.
        You can maintain another structure with the inverted relation, but it's memory consuming.






      share|improve this answer

























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        3 Answers
        3






        active

        oldest

        votes








        3 Answers
        3






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        3














        The desired result can't be achieved as dictionaries, by definition, can't contain duplicated keys.



        You can, however, do the following (which is somehow close to the output you wanted):



        from collections import defaultdict
        

        
cities = {'Berlin': {'Dan', 'John'}, 'Tokyo': {'John'}}
        
output = defaultdict(set)
        

        
for city, names in cities.items():
        
    for name in names:
        
        output[name].add(city)
        
print(output)
        
# defaultdict(<class 'set'>, {'Dan': {'Berlin'}, 'John': {'Berlin', 'Tokyo'}})





        share|improve this answer




























          3














          The desired result can't be achieved as dictionaries, by definition, can't contain duplicated keys.



          You can, however, do the following (which is somehow close to the output you wanted):



          from collections import defaultdict
          

          
cities = {'Berlin': {'Dan', 'John'}, 'Tokyo': {'John'}}
          
output = defaultdict(set)
          

          
for city, names in cities.items():
          
    for name in names:
          
        output[name].add(city)
          
print(output)
          
# defaultdict(<class 'set'>, {'Dan': {'Berlin'}, 'John': {'Berlin', 'Tokyo'}})





          share|improve this answer


























            3












            3








            3







            The desired result can't be achieved as dictionaries, by definition, can't contain duplicated keys.



            You can, however, do the following (which is somehow close to the output you wanted):



            from collections import defaultdict
            

            
cities = {'Berlin': {'Dan', 'John'}, 'Tokyo': {'John'}}
            
output = defaultdict(set)
            

            
for city, names in cities.items():
            
    for name in names:
            
        output[name].add(city)
            
print(output)
            
# defaultdict(<class 'set'>, {'Dan': {'Berlin'}, 'John': {'Berlin', 'Tokyo'}})





            share|improve this answer













            The desired result can't be achieved as dictionaries, by definition, can't contain duplicated keys.



            You can, however, do the following (which is somehow close to the output you wanted):



            from collections import defaultdict
            

            
cities = {'Berlin': {'Dan', 'John'}, 'Tokyo': {'John'}}
            
output = defaultdict(set)
            

            
for city, names in cities.items():
            
    for name in names:
            
        output[name].add(city)
            
print(output)
            
# defaultdict(<class 'set'>, {'Dan': {'Berlin'}, 'John': {'Berlin', 'Tokyo'}})






            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered Dec 31 '18 at 11:36









            DeepSpaceDeepSpace

            38.5k44470




            38.5k44470

























                2














                Other option, without dependencies and returning list of cities:



                cities = {'Berlin':{'Dan', 'John'},'Tokyo':{'John', 'Paul'}, 'Liverpool':{'John', 'Paul', 'George', 'Ringo'}, 'Colorado':{'Ringo'} }
                

                
res = {}
                
for k, v in cities.items():
                
  for e in v:
                
    res.setdefault(e,).append(k)
                

                
print(res)
                
#=> {'Dan': ['Berlin'], 'John': ['Berlin', 'Tokyo', 'Liverpool'], 'Paul': ['Tokyo', 'Liverpool'], 'Ringo': ['Liverpool', 'Colorado'], 'George': ['Liverpool']}





                share|improve this answer




























                  2














                  Other option, without dependencies and returning list of cities:



                  cities = {'Berlin':{'Dan', 'John'},'Tokyo':{'John', 'Paul'}, 'Liverpool':{'John', 'Paul', 'George', 'Ringo'}, 'Colorado':{'Ringo'} }
                  

                  
res = {}
                  
for k, v in cities.items():
                  
  for e in v:
                  
    res.setdefault(e,).append(k)
                  

                  
print(res)
                  
#=> {'Dan': ['Berlin'], 'John': ['Berlin', 'Tokyo', 'Liverpool'], 'Paul': ['Tokyo', 'Liverpool'], 'Ringo': ['Liverpool', 'Colorado'], 'George': ['Liverpool']}





                  share|improve this answer


























                    2












                    2








                    2







                    Other option, without dependencies and returning list of cities:



                    cities = {'Berlin':{'Dan', 'John'},'Tokyo':{'John', 'Paul'}, 'Liverpool':{'John', 'Paul', 'George', 'Ringo'}, 'Colorado':{'Ringo'} }
                    

                    
res = {}
                    
for k, v in cities.items():
                    
  for e in v:
                    
    res.setdefault(e,).append(k)
                    

                    
print(res)
                    
#=> {'Dan': ['Berlin'], 'John': ['Berlin', 'Tokyo', 'Liverpool'], 'Paul': ['Tokyo', 'Liverpool'], 'Ringo': ['Liverpool', 'Colorado'], 'George': ['Liverpool']}





                    share|improve this answer













                    Other option, without dependencies and returning list of cities:



                    cities = {'Berlin':{'Dan', 'John'},'Tokyo':{'John', 'Paul'}, 'Liverpool':{'John', 'Paul', 'George', 'Ringo'}, 'Colorado':{'Ringo'} }
                    

                    
res = {}
                    
for k, v in cities.items():
                    
  for e in v:
                    
    res.setdefault(e,).append(k)
                    

                    
print(res)
                    
#=> {'Dan': ['Berlin'], 'John': ['Berlin', 'Tokyo', 'Liverpool'], 'Paul': ['Tokyo', 'Liverpool'], 'Ringo': ['Liverpool', 'Colorado'], 'George': ['Liverpool']}






                    share|improve this answer












                    share|improve this answer



                    share|improve this answer










                    answered Dec 31 '18 at 11:54









                    iGianiGian

                    3,9832623




                    3,9832623























                        1














                        You can't have a dictionary with duplicate keys like @DeepSpace indicated, so for your problem I can suggest you the following alternative.
                        Use a dictionary with people's name for keys and for value the cities. And so when you want when combine the two for creating a list tuples or so on.



                        people = {"Dan": ["Berlin","San Francisco"], "Mario": ["Rome"]}
                        

                        
for name, locations in people:
                        
  #combine name with single city if needed
                        
  for city in locations:
                        
    tuple_tmp = (name,city)
                        
    #next store it, print it,...


                        This approach cons are:




                        • You need to process the values

                        • If you have city and and want to retrieve all names in this one is very slow operation.
                          You can maintain another structure with the inverted relation, but it's memory consuming.






                        share|improve this answer






























                          1














                          You can't have a dictionary with duplicate keys like @DeepSpace indicated, so for your problem I can suggest you the following alternative.
                          Use a dictionary with people's name for keys and for value the cities. And so when you want when combine the two for creating a list tuples or so on.



                          people = {"Dan": ["Berlin","San Francisco"], "Mario": ["Rome"]}
                          

                          
for name, locations in people:
                          
  #combine name with single city if needed
                          
  for city in locations:
                          
    tuple_tmp = (name,city)
                          
    #next store it, print it,...


                          This approach cons are:




                          • You need to process the values

                          • If you have city and and want to retrieve all names in this one is very slow operation.
                            You can maintain another structure with the inverted relation, but it's memory consuming.






                          share|improve this answer




























                            1












                            1








                            1







                            You can't have a dictionary with duplicate keys like @DeepSpace indicated, so for your problem I can suggest you the following alternative.
                            Use a dictionary with people's name for keys and for value the cities. And so when you want when combine the two for creating a list tuples or so on.



                            people = {"Dan": ["Berlin","San Francisco"], "Mario": ["Rome"]}
                            

                            
for name, locations in people:
                            
  #combine name with single city if needed
                            
  for city in locations:
                            
    tuple_tmp = (name,city)
                            
    #next store it, print it,...


                            This approach cons are:




                            • You need to process the values

                            • If you have city and and want to retrieve all names in this one is very slow operation.
                              You can maintain another structure with the inverted relation, but it's memory consuming.






                            share|improve this answer















                            You can't have a dictionary with duplicate keys like @DeepSpace indicated, so for your problem I can suggest you the following alternative.
                            Use a dictionary with people's name for keys and for value the cities. And so when you want when combine the two for creating a list tuples or so on.



                            people = {"Dan": ["Berlin","San Francisco"], "Mario": ["Rome"]}
                            

                            
for name, locations in people:
                            
  #combine name with single city if needed
                            
  for city in locations:
                            
    tuple_tmp = (name,city)
                            
    #next store it, print it,...


                            This approach cons are:




                            • You need to process the values

                            • If you have city and and want to retrieve all names in this one is very slow operation.
                              You can maintain another structure with the inverted relation, but it's memory consuming.







                            share|improve this answer














                            share|improve this answer



                            share|improve this answer








                            edited Dec 31 '18 at 12:48

























                            answered Dec 31 '18 at 11:50









                            IulianIulian

                            14018




                            14018






























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