Checking if value present in a nested Map using lambda expression

Question

I have a nested map as Map<String, Map<String, Boolean>> and would like to find if the inner map has at least one value as TRUE. I was able to do it using a loop but trying to do it using lambda expression

Using for loop:

        Map<String, Map<String, Boolean>> maps = new HashMap<>();
        Map<String, Boolean> test = new HashMap<>();
        test.put("test1", Boolean.FALSE);
        test.put("test2", Boolean.TRUE);
        maps.put("hey", test);
        Map<String, Boolean> testtt = new HashMap<>();
        testtt.put("test3", Boolean.FALSE);
        testtt.put("test4", Boolean.TRUE);
        maps.put("lol", testtt);
        Boolean val = Boolean.FALSE;
        for(Map.Entry<String, Map<String, Boolean>> m: maps.entrySet()){
            Map<String, Boolean> mm = m.getValue();
            for(Map.Entry<String, Boolean> mmm: mm.entrySet()){
                if(mmm.getValue()){
                    val = Boolean.TRUE;
                    break;

                }
            }
        }

        System.out.println(val);

but trying to do it using lambda expression Can you please share that attempt? — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jan 19, 2023 at 22:00
Even the loop solution can be much simpler: boolean val = false; for(Map<String, Boolean> mm: maps.values()) { if(mm.containsValue(Boolean.TRUE)) { val = true; break; } } — Holger
– Holger, Commented Jan 20, 2023 at 9:44

WJS · Accepted Answer · 2023-01-20 11:59:59Z

3

I was able to do it using a loop but trying to do it using lambda expression.

Here is one way. Here the lambda will be based on a Predicate

first you need to stream the outer maps values (which is another map) and then stream the values of those.
Then it's a matter of using anyMatch() with an identity lambda to find the first true value.

Predicate<Map<String, Map<String, Boolean>>> hasTrue = m -> m.values()
        .stream().flatMap(map -> map.values().stream()).anyMatch(a->a);

System.out.println(hasTrue.test(maps));

Prints

true

And a better way as suggested by Holger

maps.values().stream()
           .anyMatch(innerMap -> innerMap.containsValue(true))

edited Jan 20, 2023 at 11:59

answered Jan 19, 2023 at 22:04

WJS

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Comments

Ivan Krupik · Accepted Answer · 2023-01-19 21:42:44Z

2

You can try changing the loop on something like this:

Map<String, Map<String, Boolean>> maps = new HashMap<>();
boolean hasValue = maps
.values()
.stream()
.flatMap(m -> m.values().stream())
.anyMatch(b -> b.getValue());

answered Jan 19, 2023 at 21:42

Ivan Krupik

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4 Comments

WJS Over a year ago

Unfortunately, this doesn't compile. The problem is here -> anyMatch(b -> b.getValue(); Did you try to run it?

Ivan Krupik Over a year ago

I couldn't run it. I just sent it over my phone and try to help ASAP, but appreciate your comment. I will try to run it

Holger Over a year ago

Since you are streaming over values(), b is already a boolean, hence you can’t call getValue() but there is no need to do. Just anyMatch(b -> b) would do. But it’s still unnecessarily complicated. See this comment

Ivan Krupik Over a year ago

@Holger Thank you, you are right, my misspelling

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