Stream groupingBy: reducing to first element of list [duplicate]
Actually, you need to use Collectors.toMap
here instead of Collectors.groupingBy
:
Map<String, Valuta> map = getValute().stream() .collect(Collectors.toMap(Valuta::getCodice, Function.identity()));
groupingBy
is used to group elements of a Stream based on a grouping function. 2 Stream elements that will have the same result with the grouping function will be collected into a List
by default.
toMap
will collect the elements into a Map
where the key is the result of applying a given key mapper and the value is the result of applying a value mapper. Note that toMap
, by default, will throw an exception if a duplicate is encountered.
It's a bit late in the game, but try this:
Map<String, Valuta> map = getValute().stream() .collect(Collectors.groupingBy(Valuta::getCodice, Collectors.collectingAndThen( Collectors.toList(), values -> values.get(0))));
You could use Collectors.toMap(keyMappingFunction, valueMappingFunction)
Map<String, Valuta> map = list .stream() .collect(Collectors.toMap(Valuta::getCodice, v -> v));
You can replace v->v
with Function.identity()
if you find it more readable. Note that toMap
, by default, will throw an exception if a duplicate is encountered.