Can non terminal operation mark stream as ordered without actually sorting it ? (original) (raw)

Boaz Nahum boaznahum at gmail.com
Sun Apr 7 08:55:39 PDT 2013

Hi.

I have parallel unordered stream.

In some point I convert the stream to Pair<Integer, T> where *Integer *is index of element in stream. It is quite clear that each element is assigned arbitrary index, but once assigned I want it to be ordered by this index.

Sure I can do:

si.sequential().map((t)->new Pair<>(index.incrementAndGet(), t));

But I already learnt that I cant count on 'sequential()' ... :)

Or sort it: si.map((t)->new Pair<>(index.incrementAndGet(), t)).sorted((t1, t2)->t1.first.compareTo(t2.first));

But why pay the cost of sorting.

Or collect it to 'ordered' collection to protect 'sequential': si.sequential().map((t)->new Pair<>(index.incrementAndGet(), t)).collect(collector).stream();

here I pay the price of allocation Collection to hold all elements.

What i really need is somethings like this:

si.ordered().map((t)->new Pair<>(index.incrementAndGet(), t));

But unlike 'sequential()/parallel()' It cant be global.

Does making stream 'ordered' as better/worse performance than converting it to stream->collection->stream ?

I know it is rare use, But still I'm wondering.

Thanks Boaz

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