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Converting a list of objects with a map to an array of primitives

I keep finding pieces of something that I need to do, but I'm having trouble getting it. For starters, here's my object, just:

Object1
    Object2
        Map<String, Double>

What I need to do, starting with a list Object1

, get double[]

for the map values ​​given by a specific key (all objects in the list have the same N keys in the map).

Here's my starting attempt:

myList.stream().map(Object1::getObject2).map(Object2::getMyMap).map(m -> m.get(key).collect(Collectors.toCollection(ArrayList::new))

I'm not sure how to get to the primitive array from here. If it's okay so far, where do I go from here? If there is a better way to do all this, I am open to suggestions. Any help is appreciated, thanks.

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1 answer


Use .mapToDouble

to do DoubleStream

:



myList.stream()
    .map(Object1::getObject2)
    .map(Object2::getMyMap)
    .mapToDouble(m -> m.get(key))  // or throw if key is not in map
    .toArray();
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