Today’s Ruby Tuesday is on Array#sample.
Array#sample has a couple of different forms it can take.
The first form it can take is a version where no arguments are passed; in this case it returns a random element from the array it was called on, or nil if the array is empty.
1 2 3 4 5 6 7 8 9 10 | [1, 2, 3, 4, 5].sample# => 4[1, 2, 3, 4, 5].sample# => 1[1, 2, 3, 4, 5].sample# => 2[].sample# => nil[:heart, :diamond, :club, :spade].sample# => :club |
Array#sample can also take as its argument a count of the number of random items to be returned.
1 2 3 4 5 6 7 8 9 10 | [1, 2, 3, 4, 5].sample 2# => [1, 2][1, 2, 3, 4, 5].sample 2# => [2, 1][1, 2, 3, 4, 5].sample 2# => [1, 3][1, 2, 3, 4, 5].sample 2# => [3, 5][1, 2, 3, 4, 5].sample 2# => [5, 2] |
If the argument to the count is greater than, or equal to, the number of items in the array, then the array is returned.
1 2 | [:heart, :diamond, :club, :spade].sample 6# => [:heart, :diamond, :spade, :club] |
This has two subtle but important consequences. First if we call sample with a count on an empty array, an empty array is returned, instead of a nil like we would get back if we just call Array#sample with no count argument. This includes calling Array#sample with a count of zero on an empty array.
1 2 3 4 5 6 7 8 | [].sample# => nil[].sample 0# => [][].sample 1# => [][].sample 3# => [] |
Second, it shows that as we sample the array, we are not going to get duplicate elements, unless they were in the array to being with.
On both of these forms, a random number generator can also be passed. This can give us a repeatable generation sequence as we can prime the generator with a given seed.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | generatorA = Random.new 1# => #<Random:0x007f86c3925878>(1..100).to_a.sample(random: generatorA)# => 38(1..100).to_a.sample(random: generatorA)# => 13(1..100).to_a.sample(random: generatorA)# => 73generatorB = Random.new 1# => #<Random:0x007f86c497dd10>(1..100).to_a.sample(random: generatorB)# => 38(1..100).to_a.sample(random: generatorB)# => 13(1..100).to_a.sample(random: generatorB)# => 73(1..100).to_a.sample(random: generatorB)# => 10(1..100).to_a.sample(random: generatorA)# => 10(1..100).to_a.sample(4, random: generatorA)# => [76, 6, 82, 66](1..100).to_a.sample(4, random: generatorA)# => [17, 2, 79, 74](1..100).to_a.sample(4, random: generatorB)# => [76, 6, 82, 66](1..100).to_a.sample(4, random: generatorB)# => [17, 2, 79, 74] |
And if we want to pick a random card from a deck of cards, or even draw a 5 card hand we can use Array#sample on an array of “playing cards”.
1 2 3 4 5 6 7 8 | suit = [:heart, :diamond, :club, :spade]# => [:heart, :diamond, :club, :spade]rank = [:ace, 2, 3, 4, 5, 6, 7, 8, 9, :jack, :queen, :king]# => [:ace, 2, 3, 4, 5, 6, 7, 8, 9, :jack, :queen, :king]suit.product(rank).sample 1# => [[:heart, :jack]]suit.product(rank).sample 5# => [[:club, 2], [:diamond, 2], [:spade, 7], [:club, 8], [:spade, :king]] |
–Proctor