How to use Java 8 Collectors groupingBy to get a Map with a Map of the collection? -


imagine these classes

class subject {    private int id;    private type type;    private string origin;    private string name;     subject(int id, type type, string origin, string name) {       this.id = id;       this.type = type;       this.origin = origin;       this.name = name;    }     // getters , setters }  enum type {    type1,    type2 }

i have list of subject classes

list<subject> subjects = arrays.aslist(     new subject(1, type.type1, "south", "oscar"),     new subject(2, type.type2, "south", "robert"),     new subject(3, type.type2, "north", "dan"),     new subject(4, type.type2, "south", "gary"));

i result of using collectors.groupingby() map grouping first subject objects subject.origin , grouped subject.type

getting result object map<string, map<type, list<subject>>>

groupingby accepts downstream collector, can groupingby:

subjects.stream()         .collect(groupingby(                 subject::getorigin,                  groupingby(subject::gettype)             ));

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