How to map with index in Ruby?

What is the easiest way to convert

[x1, x2, x3, ... , xN]

to

[[x1, 2], [x2, 3], [x3, 4], ... , [xN, N+1]]

Solution 1:

If you're using ruby 1.8.7 or 1.9, you can use the fact that iterator methods like each_with_index, when called without a block, return an Enumerator object, which you can call Enumerable methods like map on. So you can do:

arr.each_with_index.map { |x,i| [x, i+2] }

In 1.8.6 you can do:

require 'enumerator'
arr.enum_for(:each_with_index).map { |x,i| [x, i+2] }

Solution 2:

Ruby has Enumerator#with_index(offset = 0), so first convert the array to an enumerator using Object#to_enum or Array#map:

[:a, :b, :c].map.with_index(2).to_a
#=> [[:a, 2], [:b, 3], [:c, 4]]

Solution 3:

In ruby 1.9.3 there is a chainable method called with_index which can be chained to map.

For example:

array.map.with_index { |item, index| ... }

Solution 4:

Over the top obfuscation:

arr = ('a'..'g').to_a
indexes = arr.each_index.map(&2.method(:+))
arr.zip(indexes)