The #map method on its
own allows you to interact with each item of an array, producing a new array.
[1,2,3].map { |item| item * item }
#=> [1,4,9]If you also want access to the index of the item, you'll need some help from
other enumerable methods. As of Ruby 1.9.3, you can chain on
#with_index:
[1,2,3].map.with_index { |item, index| item * index }
#=> [0,2,6]This method has the added benefit of allowing you to specify the starting value
of the index. It normally starts with 0, but you could just as easily start
at 1:
[1,2,3].map.with_index(1) { |item, index| item * index }
#=> [1,4,9]