Sort an array of keys with an array of order

sort_array_by_other_array.rb

# input data

sort = [  3,  1,  4,  2 ]
ary  = [ :a, :b, :c, :d ]
# the index value should be in result, too (with id+1 because they can be DB indices)



### sort array represents **position** of item in `ary`
#
# unsorted: 3 => a, 1 => b, 4 => c, 2 => d
#   sorted: 1 => b, 2 => d, 3 => a, 4 => b

ary.
  map_with_index{|k,i| [i+1, k] }. # in ruby 1.9 can be replaced with `.map.with_index`
  zip(sort).
  sort_by{|e| e[1] }.
  map{|e| e[0] }



### sort array represents **index** of item in `ary`
#
# (index in ary reduced by 1)
# ary map: ary[2] => c, ary[0] => a, ary[3] => d, ary[1] => b
#  result: 3      => c, 1      => a, 4      => d, 2      => b

sort.map{ |pos|
  [pos] + ary.select{|elem| ary.index(elem) == (pos-1) }
}