Ruby Language Iteration Iteration with index


Example

Sometimes you want to know the position (index) of the current element while iterating over an enumerator. For such purpose, Ruby provides the with_index method. It can be applied to all the enumerators. Basically, by adding with_index to an enumeration, you can enumerate that enumeration. Index is passed to a block as the second argument.

[2,3,4].map.with_index { |e, i| puts "Element of array number #{i} => #{e}" }
#Element of array number 0 => 2
#Element of array number 1 => 3
#Element of array number 2 => 4
#=> [nil, nil, nil]

with_index has an optional argument – the first index which is 0 by default:

[2,3,4].map.with_index(1) { |e, i| puts "Element of array number #{i} => #{e}" }
#Element of array number 1 => 2
#Element of array number 2 => 3
#Element of array number 3 => 4
#=> [nil, nil, nil]

There is a specific method each_with_index. The only difference between it and each.with_index is that you can't pass an argument to that, so the first index is 0 all the time.

[2,3,4].each_with_index { |e, i| puts "Element of array number #{i} => #{e}" }
#Element of array number 0 => 2
#Element of array number 1 => 3
#Element of array number 2 => 4
#=> [2, 3, 4]