How to get a randomly selected hash key in Perl 6?

Question

A quick and hopefully simple question:

I need tools to randomly select from a given set of hash keys. The perl6.org documentation on neither rand nor hash offers a lot of advice.

my %a = 1,2,3,4,5,6; 

Given the foregoing,

 %a.keys; 

returns (5 1 3) , and if I just try

 %a.rand; 

I get a pseudo-random float, and not just any one key.

In the end, I collected %a.keys[Int(%a.elems.rand)] , but was hoping for something simpler.

Answer 1

Use pick or roll e.g.

 %a.keys.pick 

Answer 2

As always, Christoph's answer is correct (he knows Perl 6 well). Nevertheless, I thought that I would work a little with pick and roll can be easily confused in the first place.

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If you only need one random key, pick and roll seem the same and can be used interchangeably:

 my $rand-keyA = %a.keys.pick; my $rand-keyB = %a.keys.roll; 

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However, think pick as “I have N things and I take them out of the container, and as soon as they disappear, they left (for this choice)” compared to roll as “I have an N-way game that I ride "

 say %a.keys.pick(2); # (5 3) say %a.keys.pick(2); # (3 1) say %a.keys.pick(5); # (3 5 1) no more, because there were only three to pick from say %a.keys.pick(10); # (3 1 5) say %a.keys.roll(5); # (1 5 1 5 3) as many "rolls" as you request say %a.keys.roll(10); # (5 5 1 1 5 5 3 1 3 1) 

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pick(*) is an easy way to create a random list of orders from an array without having to know how many elements are in it:

 my @array = <foo bar baz foobar>; @array.pick(*); # (bar foobar baz foo) 

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roll(*) is an easy way to create an infinite list whose elements were randomly selected from the original array:

 my @rolls = @array.roll(*); say @rolls[0]; # foobar say @rolls[10]; # bar say @rolls[351]; # baz say @rolls[19123]; # foobar say @rolls[1000000]; # bar say @rolls[1000001]; # bar say @rolls[1000002]; # foo