How to map with index in Ruby?

Question

What is the easiest way to convert

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

to

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

Answer 1

Over the top obfuscation:

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

Answer 2

A fun, but useless way to do this:

az  = ('a'..'z').to_a
azz = az.map{|e| [e, az.index(e)+2]}

Answer 3

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]]

Answer 4

module Enumerable
  def map_with_index(&block)
    i = 0
    self.map { |val|
      val = block.call(val, i)
      i += 1
      val
    }
  end
end

["foo", "bar"].map_with_index {|item, index| [item, index] } => [["foo", 0], ["bar", 1]]