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
– senia, Commented Sep 7, 2013 at 15:59

Arseniy Zhizhelev · Accepted Answer · 2013-09-07 18:33:01Z

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 7, 2013 at 18:33

Arseniy Zhizhelev

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René Höhle · Accepted Answer · 2014-09-10 08:38:24Z

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

edited Sep 10, 2014 at 8:38

René Höhle

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answered Sep 10, 2014 at 8:22

haha1903

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Garrett Hall · Accepted Answer · 2013-09-07 16:45:47Z

1

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

answered Sep 7, 2013 at 16:45

Garrett Hall

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Arseniy Zhizhelev · Accepted Answer · 2013-09-07 18:42:09Z

1

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 7, 2013 at 18:42

Arseniy Zhizhelev

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