From: Colin Bartlett <colinb2r@...>
Date: 2010-12-27T00:56:01+09:00
Subject: Re: array index inside map function

On Sun, Dec 26, 2010 at 8:34 AM, Siddharth Venkatesan
<neotamizhan@gmail.com> wrote:
> how can i access the index of the element inside the map argument block?
>   "101010,234,876".split(",").map {|c| get_something(c)}
> ...

On Sun, Dec 26, 2010 at 9:13 AM, Siddharth Venkatesan
<neotamizhan@gmail.com> wrote:
> All of the three solution taught me something. I think i'll go with .map.with_index.
> That looks concise.

There is also the slightly less concise and elegant but possibly
somewhat faster:
ii = -1; "101010,234,876".split(",").map {|c| ii += 1; get_something(c)}

                                                user  system  total    real
Ruby: version=1.9.1; platform=i486-linux;

  ary1 = ary.map.with_index { |e, i| 355 }      2.780  0.000  2.780  ( 2.787)
  j = -1; ary2 = ary.map { |e| j += 1; 113 }    2.550  0.010  2.560  ( 2.556)

  ary3 = ari.map!.with_index { |e, i| 355 }     2.590  0.000  2.590  ( 2.591)
  j = -1; ary4 = arj.map! { |e| j += 1; 113 }   2.150  0.000  2.150  ( 2.150)

Ruby: version=1.9.1; platform=i386-mingw32;

  ary1 = ary.map.with_index { |e, i| 355 }      2.870  0.000  2.870  ( 2.893)
  j = -1; ary2 = ary.map { |e| j += 1; 113 }    2.028  0.016  2.044  ( 2.045)

  ary3 = ari.map!.with_index { |e, i| 355 }     2.761  0.000  2.761  ( 2.772)
  j = -1; ary4 = arj.map! { |e| j += 1; 113 }   1.997  0.000  1.997  ( 2.008)


*** code for benchmarks

class Array   # so we can tell if same array and see changes
  def ps( name = '?' )
    puts "#{name}: <oid=#{object_id}: [0] = #{self[0].inspect}>"
  end
end

require "benchmark"
kt = 100_000
nn = 100
ary = Array.new( nn, 42 )
ari = Array.new( nn, 22 ); arj = Array.new( nn, 7 )
puts
puts "Ruby: version=#{RUBY_VERSION}; platform=#{RUBY_PLATFORM};"
puts
ary.ps('ary'); ari.ps('ari'); arj.ps('arj')
puts
ary1 = ary2 = ary3 = ary4 = nil
w = 50
Benchmark.bmbm( w ) do |bm|
  bm.report( "ary1 = ary.map.with_index { |e, i| 355 }" ) {
   kt.times { ary1 = ary.map.with_index { |e, i| 355 } } }
  bm.report( "j = -1; ary2 = ary.map { |e| j += 1; 113 }" ) {
   kt.times { j = -1; ary2 = ary.map { |e| j += 1; 113 } } }
  bm.report( "ary3 = ari.map!.with_index { |e, i| 355 }" ) {
   kt.times { ary3 = ari.map!.with_index { |e, i| 355 } } }
  bm.report( "j = -1; ary4 = arj.map! { |e| j += 1; 113 }" ) {
   kt.times { j = -1; ary4 = arj.map! { |e| j += 1; 113 } } }
end
puts
ary.ps('ary'); ari.ps('ari'); arj.ps('arj')
puts
ary1.ps('ary1'); ary2.ps('ary2'); ary3.ps('ary3'); ary4.ps('ary4')