Efficient way to get a random element in Scala?

Question

What is an efficient way to get a random element from a collection in Scala? There's a related question here, but like one of the comments pointed out, "[that] question does not specify any efficiency needs".

In case `size` method is efficient you should use `apple(randomIndexLessThanSize)`. In general there is no such method: for instance you can't get fair random element from infinite collection. — senia, Sep 07 '13 at 15:59

score 6 · Accepted Answer · answered Sep 07 '13 at 18:33

6

An arbitrary collection cannot be accessed in constant time. So you need some special collection with the desired property. For instance — Vector or Array. See Performance Characteristics of collections for others.

answered Sep 07 '13 at 18:33

Arseniy Zhizhelev

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score 2 · Answer 2 · edited Sep 10 '14 at 08:38

2

util.Random.shuffle(List.range(1,100)) take 3

edited Sep 10 '14 at 08:38

René Höhle

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answered Sep 10 '14 at 08:22

haha1903

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score 1 · Answer 3 · answered Sep 07 '13 at 16:45

1

Use a collection with a constant-time size() and get() method.

answered Sep 07 '13 at 16:45

Garrett Hall

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score 1 · Answer 4 · answered Sep 07 '13 at 18:42

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If you need random order of all collection elements, then Random.shuffle is what you need. (You'd better convert the original collection to array to avoid forward and backward conversion.)

answered Sep 07 '13 at 18:42

Arseniy Zhizhelev

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Efficient way to get a random element in Scala?

4 Answers4

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