What is the best/efficient way to convert HashSet of type <String> to HashSet of type <Long> ?
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Manos Nikolaidis
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Prasad Revanaki
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may be by trying out some actual code? try lambda expressions from java 8. would give you the solution in single line – sidgate Oct 30 '15 at 09:35
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Set<Long> longSet = stringSet.stream().map(s-> Long.parseLong(s))
.collect(Collectors.toSet());
I haven't tried it out but should work
sidgate
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3`s-> Long.parseLong(s)` could be a method reference: `Long::parseLong`. – Christoffer Hammarström Oct 30 '15 at 10:39
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An improvement to sidgate's answer [when working with really large sets]: you can use parallelStream() it should be more efficient on large set, and replace Long.parseLong(s) with method reference.
Set<Long> longSet = stringSet.parallelStream()
.map(Long::parseLong)
.collect(Collectors.toSet());
[Edit] As noted in the comments, use parallelStream() only when working with really large sets, as it adds considerable amount of overhead.
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ttarczynski
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`parallelStream` though useful, shouldn't be used for such simpler use case. http://zeroturnaround.com/rebellabs/java-parallel-streams-are-bad-for-your-health/ – sidgate Oct 30 '15 at 10:26
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No, don't use `parallelStream` unless you have more than 10,000-100,000 elements and have measured that using `parallelStream` will be an improvement. – Christoffer Hammarström Oct 30 '15 at 10:39
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