how to efficiently remove null from the list?

Question

In a scenario where a map of coreValues contains: Value 1 -> List("1", "2", null, "3") I want to filter out null values from the list, i have below solution:

 boolean hasCoreValues = false;
 Optional<Map<String,List<String>> coreValues = buildCoreValuesMap(core); 
 hasCoreValues = corevalues.map(cv -> {
    final List<String> values = cv.getOrDefault(value, Immutable.of())
    values.removeAll(singletonList(null));
    return !values.isEmpty();
 }).orElse(false);



public Optional<Map<String, List<String>>> buildCoreValuesMap(String core) {
        return Optional.ofNullable(context.selectFrom(DataStorage)
                .where(DataStorage.CORE.in(core))
                .fetchGroups(DataStorage.CORE,
                        DataStorage.VALUES));
    }

is there a better way to do it without going thru the list again to remove the null?

values.removeAll(singletonList(null)) i am using the method to remove null, its not a duplicate question. My question is to how to remove null without iterating twice. — MikasaAckerman, Oct 07 '19 at 23:46

Ryuzaki L · Answer 1 · 2019-10-07T23:36:36.227

4

If you just want to remove all null in List<String> from coreValues, then just iterate Map and remove all null values from list using removeIf

coreValues.forEach((k,v)-> v.removeIf(Objects::isNull));

edited Oct 07 '19 at 23:36

answered Oct 07 '19 at 23:31

Ryuzaki L

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Of course, if you wrote `buildCoreValuesMap()` you might employ a filter to keep them out in the first place. – WJS Oct 07 '19 at 23:45
can i avoid iterating map twice? – MikasaAckerman Oct 07 '19 at 23:45
can you show the first place where you are iterating map ? @MikasaAckerman – Ryuzaki L Oct 07 '19 at 23:46
Well, I can't provide an answer now because the question has been marked as a duplicate. But Deadpool could tag on an edit and probably show you how to do it. – WJS Oct 07 '19 at 23:47
In order to do that OP needs to show the code of `buildCoreValuesMap` @WJS – Ryuzaki L Oct 07 '19 at 23:49
@Deadpool Yes I know. But you could probably gen up a simple example which he might be able to adapt. – WJS Oct 07 '19 at 23:49
sorry it is not really clear to me, until and unless he shows the code, because i don't know the internal logic. But you are always welcome to edit my answer with valuable information @WJS – Ryuzaki L Oct 07 '19 at 23:53
updated the question – MikasaAckerman Oct 07 '19 at 23:55
actually i never used this library @MikasaAckerman which library is this ? – Ryuzaki L Oct 08 '19 at 00:01
jooq library is being used here – MikasaAckerman Oct 08 '19 at 00:27

how to efficiently remove null from the list?

1 Answers1