I have a list of map for which i want to group them by name
List<Map> allObjs = new ArrayList<Map>();
Map<String, Object> src = new HashMap();
src.put("name", "asset1");
src.put("description", "desc1" );
src.put("definition", "def1" );
Map<String, Object> src2 = new HashMap();
src2.put("name", "asset1");
src2.put("description", "desc2" );
src2.put("definition", "def2" );
allObjs.add(src);
allObjs.add(src2);
I tried grouping them by
Map<Object, List<Map>> result = allObjs.stream().collect(Collectors.groupingBy(p -> p.get("name")));
What i want is
{
name=asset1,
description=["desc1","desc2"],
definition=["def1","def2"]
}
I want all the other keys to be grouped in a list But what i got is
{asset1=[
{name=asset1, description=desc1, definition=def2},
{name=asset1, description=desc2, definition=def2}
]
}
How do i group all the other keys except name to a list like expected above?
You can use groupBy
with mapping
to get the desired result, just values would be of single type only,
Map<String, Set<String>> collect1 = allObjs.stream()
.flatMap(m -> m.entrySet().stream())
.collect(groupingBy(Map.Entry::getKey, mapping(Map.Entry::getValue, toSet())));
Result:
{
name=[asset1],
description=[desc1,desc2],
definition=[def1,def2]
}
groupingBy
will group the items based on a key. It does not do a merge of two maps. This is one of the ugly ways to achieve what you want.
Given
List<Map<String, String>> allObjs = new ArrayList<>();
Map<String, String> src = new HashMap();
src.put("name", "asset1");
src.put("description", "desc1" );
src.put("definition", "def1" );
Map<String, String> src2 = new HashMap();
src2.put("name", "asset1");
src2.put("description", "desc2" );
src2.put("definition", "def2" );
allObjs.add(src);
allObjs.add(src2);
One way to do is this. Create two classes, representing existing structure and final output structure
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class SomeClass {
private String name;
private String description;
private String definition;
}
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class NewClass {
private String name;
private List<String> description;
private List<String> definition;
}
Then this code should get the output u desired
final List<NewClass> collect = allObjs.stream()
.map(entry -> new SomeClass(entry.get("name"), entry.get("description"), entry.get("definition")))
.collect(Collectors.toList())
.stream()
.collect(Collectors.groupingBy(SomeClass::getName))
.entrySet()
.stream()
.map(entry -> {
final List<String> descriptions = entry.getValue().stream().map(SomeClass::getDescription).collect(Collectors.toList());
final List<String> definitions = entry.getValue().stream().map(SomeClass::getDefinition).collect(Collectors.toList());
return new NewClass(entry.getKey(), descriptions, definitions);
}).collect(Collectors.toList());
End result will be a list of type NewClass . Each entry in the list will have the desired output with a unique key. You need to incorporate a lot of null checks since it is a Map we are dealing with.
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