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

User · Answer

Here are two more options for 1 8 6  or 1 9  without using enumerator     Fun with functional arr     a    g   to a arr zip   2   arr length 2   to a      gt     a   2     b   3     c   4     d   5     e   6     f   7     g   8      The simplest n   1 arr map   c   c  n  1        gt     a   2     b   3     c   4     d   5     e   6     f   7     g   8

User · Answer

I have always enjoyed the syntax of this style   a    1  2  3  4  a each with index map    el  index  el   index       gt   1  3  5  7    Invoking each with index gets you an enumerator you can easily map over with your index available

User · Answer

A fun  but useless way to do this   az      a    z   to a azz   az map  e   e  az index e  2

User · Answer

a    1  2  3  p  a   2   a size 2  to a  transpose

User · Answer

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    gt     a  2     b  3     c  4

User · Answer

Over the top obfuscation   arr     a    g   to a indexes   arr each index map  amp 2 method      arr zip indexes

User · Answer

I often do this   arr     a    b    c     0   arr length  map do  int     arr int   int   2  end     gt     a   2     b   3     c   4     Instead of directly iterating over the elements of the array  you re iterating over a range of integers and using them as the indices to retrieve the elements of the array

User · Answer

module Enumerable   def map with index  amp 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      gt     foo   0     bar   1

User · Answer

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

User · Answer

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

[ruby] How to map with index in Ruby?

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