How to map with index in Ruby?

ruby arrays indexing
Misha Moroshko picture Misha Moroshko · Jan 15, 2011 · Viewed 230k times · Source

What is the easiest way to convert 

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

to

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

Answer

sepp2k picture sepp2k · Jan 15, 2011

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] }

Related questions

Get index of array element faster than O(n)

Given I have a HUGE array, and a value from it. I want to get index of the value in array. Is there any other way, rather then call Array#index to get it? The problem comes from the need …

Read More
In Ruby, what is the cleanest way of obtaining the index of the largest value in an array?

If a is the array, I want a.index(a.max), but something more Ruby-like. It should be obvious, but I'm having trouble finding the answer at so and elsewhere. Obviously, I am new to Ruby.

Read More
Ruby: How to find the index of the minimum array element?

Is there any way to rewrite this more elegant? I think, that it's a bad piece of code and should be refactored. >> a = [2, 4, 10, 1, 13] => [2, 4, 10, 1, 13] >> index_of_minimal_value_in_array = a.index(a.min) => 3

Read More