How do you select every nth item in an array?

You could also use step:

n = 2
a = ["cat", "dog", "mouse", "tiger"]
b = (n - 1).step(a.size - 1, n).map { |i| a[i] }

You can use Enumerable#each_slice:

["cat", "dog", "mouse", "tiger"].each_slice(2).map(&:last)
# => ["dog", "tiger"]

Update:

As mentioned in the comment, last is not always suitable, so it could be replaced by first, and skipping first element:

["cat", "dog", "mouse", "tiger"].drop(1).each_slice(2).map(&:first)

Unfortunately, making it less elegant.

IMO, the most elegant is to use .select.with_index, which Nakilon suggested in his comment:

["cat", "dog", "mouse", "tiger"].select.with_index{|_,i| (i+1) % 2 == 0}

How about this -

arr = ["cat", "dog", "mouse", "tiger"]
n = 2
(0... arr.length).select{ |x| x%n == n-1 }.map { |y| arr[y] } 
    #=> ["dog", "tiger"]

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