Parsing a list out of lists using Java Streams

Question

I have a list of products. Each product holds another list of ingredients. How can I use Streams in order to get a list of all ingredients from all products?

products.stream()
        .map(Product::getIngredients())
        .filter(i -> !i.isEmpty())
        .distinct()
        .collect(Collectors.toList());

Above the code as far as I got, so far I'm just getting a list with sublists...

What's the right way to do this?

Thanks a lot!

Look at Stream.flatMap: docs.oracle.com/javase/8/docs/api/java/util/stream/… — tsolakp
– tsolakp, Commented Jan 11, 2018 at 21:10

Eugene · Accepted Answer · 2018-01-12 07:48:34Z

7

Just use flatMap :

products.stream()
        .flatMap(product -> product.getIngredients().stream())
        .distinct()
        .collect(Collectors.toList());

edited Jan 12, 2018 at 7:48

Eugene

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answered Jan 11, 2018 at 21:11

Schidu Luca

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4 Comments

Andrew Rueckert Over a year ago

That'd have to be .flatMap(product -> product.getIngredients().stream())

shmosel Over a year ago

Or .map(Product::getIngredients).flatMap(List::stream).

Eugene Over a year ago

@SchiduLuca you btw need to explicitly tell OP that distinct requires hashcode/equals overridden... which you don't know if it's an option or not. otherwise plus one

shmosel Over a year ago

@Eugene It's worth a mention perhaps, but it's not at all relevant to the question or answer.

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