Collecting occurrences in a HashMap with streams





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I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.



Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:



    Map<String, Integer> freq = new HashMap<>();


Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:



    foxes.stream()

    .map(Fox::getColor)

    .forEach()

    //...(continued later on);


, where foxes is a List.



My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then



    freq.put(Fox::getName, 1)


else



    freq.replace(Fox::getName, freq.get(Fox::getName) + 1)


How should I put it together?






java java-8 hashmap java-stream method-reference







share|improve this question

























  • IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.

    – Naman
    Jan 5 at 1:45




















1















I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.



Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:



    Map<String, Integer> freq = new HashMap<>();


Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:



    foxes.stream()

    .map(Fox::getColor)

    .forEach()

    //...(continued later on);


, where foxes is a List.



My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then



    freq.put(Fox::getName, 1)


else



    freq.replace(Fox::getName, freq.get(Fox::getName) + 1)


How should I put it together?






java java-8 hashmap java-stream method-reference







share|improve this question

























  • IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.

    – Naman
    Jan 5 at 1:45
















1












1








1


1






I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.



Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:



    Map<String, Integer> freq = new HashMap<>();


Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:



    foxes.stream()

    .map(Fox::getColor)

    .forEach()

    //...(continued later on);


, where foxes is a List.



My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then



    freq.put(Fox::getName, 1)


else



    freq.replace(Fox::getName, freq.get(Fox::getName) + 1)


How should I put it together?






java java-8 hashmap java-stream method-reference







share|improve this question
















I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.



Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:



    Map<String, Integer> freq = new HashMap<>();


Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:



    foxes.stream()

    .map(Fox::getColor)

    .forEach()

    //...(continued later on);


, where foxes is a List.



My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then



    freq.put(Fox::getName, 1)


else



    freq.replace(Fox::getName, freq.get(Fox::getName) + 1)


How should I put it together?






java java-8 hashmap java-stream method-reference




java java-8 hashmap java-stream method-reference






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Jan 4 at 18:49









Jacob G.

16.9k52466




16.9k52466










asked Jan 4 at 18:43









Csongi NagyCsongi Nagy

19119




19119













  • IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.

    – Naman
    Jan 5 at 1:45





















  • IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.

    – Naman
    Jan 5 at 1:45



















IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.

– Naman
Jan 5 at 1:45







IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.

– Naman
Jan 5 at 1:45














1 Answer
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oldest

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6














I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:



 Map<String, Long> result = foxes.stream()

      .collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));


This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.



foxes.stream()

     .collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));





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    1 Answer
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    active

    oldest

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    oldest

    votes






    active

    oldest

    votes









    6














    I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:



     Map<String, Long> result = foxes.stream()
    
      .collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));


    This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.



    foxes.stream()
    
     .collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));





    share|improve this answer






























      6














      I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:



       Map<String, Long> result = foxes.stream()
      
      .collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));


      This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.



      foxes.stream()
      
     .collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));





      share|improve this answer




























        6












        6








        6







        I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:



         Map<String, Long> result = foxes.stream()
        
      .collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));


        This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.



        foxes.stream()
        
     .collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));





        share|improve this answer















        I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:



         Map<String, Long> result = foxes.stream()
        
      .collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));


        This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.



        foxes.stream()
        
     .collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));






        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited Jan 4 at 18:48

























        answered Jan 4 at 18:44









        AomineAomine

        42.8k74778




        42.8k74778
































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