generating map from list of objects having a map using java lambda8











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8
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I've an object,



class Object2{
String name;
String id;
Map<String, String> customData;
}

class Object1{
List<Object2> obj1List;
}


I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.










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    up vote
    8
    down vote

    favorite












    I've an object,



    class Object2{
    String name;
    String id;
    Map<String, String> customData;
    }

    class Object1{
    List<Object2> obj1List;
    }


    I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.










    share|improve this question









    New contributor




    sar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.






















      up vote
      8
      down vote

      favorite









      up vote
      8
      down vote

      favorite











      I've an object,



      class Object2{
      String name;
      String id;
      Map<String, String> customData;
      }

      class Object1{
      List<Object2> obj1List;
      }


      I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.










      share|improve this question









      New contributor




      sar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      I've an object,



      class Object2{
      String name;
      String id;
      Map<String, String> customData;
      }

      class Object1{
      List<Object2> obj1List;
      }


      I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.







      java lambda java-8 java-stream






      share|improve this question









      New contributor




      sar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question









      New contributor




      sar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|improve this question




      share|improve this question








      edited 6 hours ago









      Aomine

      34.1k62859




      34.1k62859






      New contributor




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      asked 6 hours ago









      sar

      411




      411




      New contributor




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      New contributor





      sar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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          3 Answers
          3






          active

          oldest

          votes

















          up vote
          5
          down vote













          Here's a way with lambdas and Java 8:



          Map<String, String> map = new LinkedHashMap<>();
          object1List.forEach(o1 ->
          o1.getObject2List().forEach(o2 -> map.putAll(o2.getCustomData())));





          share|improve this answer





















          • weird naming convention in the question, but I guess you meant getObject1List()
            – nullpointer
            1 hour ago


















          up vote
          3
          down vote













          Use flatMap and toMap as follows:



          List<Object1> source = ...
          Map<String, String> result =
          source.stream()
          .flatMap(e -> e.getObj1List().stream()
          .flatMap(a -> a.getCustomData().entrySet().stream()))
          .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));


          or if you're dealing with a single Object1 object:



          Object1 myObj = ...
          Map<String, String> result =
          myObj.getObj1List()
          .stream()
          .flatMap(a -> a.getCustomData().entrySet().stream())
          .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));





          share|improve this answer






























            up vote
            3
            down vote













            Alternatively, you can perform Stream.flatMap and then use Map.putAll as



            List<Object1> object1s = new ArrayList<>(); // initialise as you would
            Map<String, String> finalCustomData = new LinkedHashMap<>();
            object1s.stream() // Stream<Object1>
            .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>
            .map(Object2::getCustomData) // Stream<Map<String, String>>
            .forEach(finalCustomData::putAll);





            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








              up vote
              5
              down vote













              Here's a way with lambdas and Java 8:



              Map<String, String> map = new LinkedHashMap<>();
              object1List.forEach(o1 ->
              o1.getObject2List().forEach(o2 -> map.putAll(o2.getCustomData())));





              share|improve this answer





















              • weird naming convention in the question, but I guess you meant getObject1List()
                – nullpointer
                1 hour ago















              up vote
              5
              down vote













              Here's a way with lambdas and Java 8:



              Map<String, String> map = new LinkedHashMap<>();
              object1List.forEach(o1 ->
              o1.getObject2List().forEach(o2 -> map.putAll(o2.getCustomData())));





              share|improve this answer





















              • weird naming convention in the question, but I guess you meant getObject1List()
                – nullpointer
                1 hour ago













              up vote
              5
              down vote










              up vote
              5
              down vote









              Here's a way with lambdas and Java 8:



              Map<String, String> map = new LinkedHashMap<>();
              object1List.forEach(o1 ->
              o1.getObject2List().forEach(o2 -> map.putAll(o2.getCustomData())));





              share|improve this answer












              Here's a way with lambdas and Java 8:



              Map<String, String> map = new LinkedHashMap<>();
              object1List.forEach(o1 ->
              o1.getObject2List().forEach(o2 -> map.putAll(o2.getCustomData())));






              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered 5 hours ago









              Federico Peralta Schaffner

              21.7k33369




              21.7k33369












              • weird naming convention in the question, but I guess you meant getObject1List()
                – nullpointer
                1 hour ago


















              • weird naming convention in the question, but I guess you meant getObject1List()
                – nullpointer
                1 hour ago
















              weird naming convention in the question, but I guess you meant getObject1List()
              – nullpointer
              1 hour ago




              weird naming convention in the question, but I guess you meant getObject1List()
              – nullpointer
              1 hour ago












              up vote
              3
              down vote













              Use flatMap and toMap as follows:



              List<Object1> source = ...
              Map<String, String> result =
              source.stream()
              .flatMap(e -> e.getObj1List().stream()
              .flatMap(a -> a.getCustomData().entrySet().stream()))
              .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));


              or if you're dealing with a single Object1 object:



              Object1 myObj = ...
              Map<String, String> result =
              myObj.getObj1List()
              .stream()
              .flatMap(a -> a.getCustomData().entrySet().stream())
              .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));





              share|improve this answer



























                up vote
                3
                down vote













                Use flatMap and toMap as follows:



                List<Object1> source = ...
                Map<String, String> result =
                source.stream()
                .flatMap(e -> e.getObj1List().stream()
                .flatMap(a -> a.getCustomData().entrySet().stream()))
                .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));


                or if you're dealing with a single Object1 object:



                Object1 myObj = ...
                Map<String, String> result =
                myObj.getObj1List()
                .stream()
                .flatMap(a -> a.getCustomData().entrySet().stream())
                .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));





                share|improve this answer

























                  up vote
                  3
                  down vote










                  up vote
                  3
                  down vote









                  Use flatMap and toMap as follows:



                  List<Object1> source = ...
                  Map<String, String> result =
                  source.stream()
                  .flatMap(e -> e.getObj1List().stream()
                  .flatMap(a -> a.getCustomData().entrySet().stream()))
                  .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));


                  or if you're dealing with a single Object1 object:



                  Object1 myObj = ...
                  Map<String, String> result =
                  myObj.getObj1List()
                  .stream()
                  .flatMap(a -> a.getCustomData().entrySet().stream())
                  .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));





                  share|improve this answer














                  Use flatMap and toMap as follows:



                  List<Object1> source = ...
                  Map<String, String> result =
                  source.stream()
                  .flatMap(e -> e.getObj1List().stream()
                  .flatMap(a -> a.getCustomData().entrySet().stream()))
                  .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));


                  or if you're dealing with a single Object1 object:



                  Object1 myObj = ...
                  Map<String, String> result =
                  myObj.getObj1List()
                  .stream()
                  .flatMap(a -> a.getCustomData().entrySet().stream())
                  .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));






                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited 6 hours ago

























                  answered 6 hours ago









                  Aomine

                  34.1k62859




                  34.1k62859






















                      up vote
                      3
                      down vote













                      Alternatively, you can perform Stream.flatMap and then use Map.putAll as



                      List<Object1> object1s = new ArrayList<>(); // initialise as you would
                      Map<String, String> finalCustomData = new LinkedHashMap<>();
                      object1s.stream() // Stream<Object1>
                      .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>
                      .map(Object2::getCustomData) // Stream<Map<String, String>>
                      .forEach(finalCustomData::putAll);





                      share|improve this answer

























                        up vote
                        3
                        down vote













                        Alternatively, you can perform Stream.flatMap and then use Map.putAll as



                        List<Object1> object1s = new ArrayList<>(); // initialise as you would
                        Map<String, String> finalCustomData = new LinkedHashMap<>();
                        object1s.stream() // Stream<Object1>
                        .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>
                        .map(Object2::getCustomData) // Stream<Map<String, String>>
                        .forEach(finalCustomData::putAll);





                        share|improve this answer























                          up vote
                          3
                          down vote










                          up vote
                          3
                          down vote









                          Alternatively, you can perform Stream.flatMap and then use Map.putAll as



                          List<Object1> object1s = new ArrayList<>(); // initialise as you would
                          Map<String, String> finalCustomData = new LinkedHashMap<>();
                          object1s.stream() // Stream<Object1>
                          .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>
                          .map(Object2::getCustomData) // Stream<Map<String, String>>
                          .forEach(finalCustomData::putAll);





                          share|improve this answer












                          Alternatively, you can perform Stream.flatMap and then use Map.putAll as



                          List<Object1> object1s = new ArrayList<>(); // initialise as you would
                          Map<String, String> finalCustomData = new LinkedHashMap<>();
                          object1s.stream() // Stream<Object1>
                          .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>
                          .map(Object2::getCustomData) // Stream<Map<String, String>>
                          .forEach(finalCustomData::putAll);






                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 1 hour ago









                          nullpointer

                          37.4k1072145




                          37.4k1072145






















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                              sar is a new contributor. Be nice, and check out our Code of Conduct.












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