How to print out a random number between a range?

Question

I've the following but it doesn't work:

<%= (5..30).sample %>

score 111 · Accepted Answer · answered Nov 18 '11 at 00:21

111

Give this a shot.

<%= [*5..30].sample %>

...or...

<%= rand(5..30) %>

answered Nov 18 '11 at 00:21

alex

6

The first solution is inefficient. Good thing it's not a random number between 5 and a million... The second solution works only in Ruby 1.9.3. This question has been answered before: http://stackoverflow.com/questions/198460/how-to-get-a-random-number-in-ruby – Marc-André Lafortune Nov 18 '11 at 06:44
@Marc-AndréLaortune: Yeah, I agree, on all things. I'll throw in my close vote. – alex Nov 18 '11 at 06:56
3

Rand is much more efficient – Erowlin Aug 03 '13 at 11:38

score 6 · Answer 2 · answered Nov 18 '11 at 00:21

6

This would generate a random number in that range:

5 + rand(25)

Simply add the min to the rand(max-min).

answered Nov 18 '11 at 00:21

mduvall

score 6 · Answer 3 · answered Nov 18 '11 at 00:21

6

Range has no #sample method. Use the one from Array instead.

<%= (5..30).to_a.sample %>

answered Nov 18 '11 at 00:21

Guilherme Bernal

stephenmurdoch · Answer 4 · 2011-11-18T12:15:21.877

3

for 1 random number:

a = (5...30).sort_by{rand}[1]
# => 7

It seems more verbose than what others have suggested, but from here, it's easy to pick three random unique numbers from the same range:

a = (5...30).sort_by{rand}[1..3]
# => [19, 22, 28]

Or 20:

a = (5...30).sort_by{rand}[1..20]
# => [7, 12, 16, 14, 13, 15, 22, 17, 24, 19, 20, 10, 21, 26, 29, 9, 23, 27, 8, 18]

Might come in useful for someone who needs to display 5 random foos in their sidebar

EDIT: Thanks to Marc-Andre Lafortune, I discovered that the following is much better:

a=[*5..30].sample(3)

edited Nov 18 '11 at 12:15

answered Nov 18 '11 at 00:52

stephenmurdoch

1

Terribly inefficient! Your solution is O(n log n) instead of a solution in O(1)! Use `Array#sample` if you need many random samples from an array. – Marc-André Lafortune Nov 18 '11 at 06:47
thanks @Marc-Andre, you learn something new everyday. I updated my answer with something based on your suggestion – stephenmurdoch Nov 18 '11 at 12:15

4 Answers4