How to sort an array in Ruby to a particular order?

Question

I want to sort an array in particular order given in another array.

EX: consider an array

a=[\"one\", \"two\", \"three\"]
b=[\"two\", \"one\", \"thr         


        

Answer 1

If b includes all elements of a and if elements are unique, then:

puts b & a

Answer 2

Assuming a is to be sorted with respect to order of elements in b

sorted_a = 
a.sort do |e1, e2|
  b.index(e1) <=> b.index(e2)
end

I normally use this to sort error messages in ActiveRecord in the order of appearance of fields on the form.

Answer 3

Array#sort_by is what you're after.

a.sort_by do |element|
  b.index(element)
end

More scalable version in response to comment:

a=["one", "two", "three"]
b=["two", "one", "three"]

lookup = {}
b.each_with_index do |item, index|
  lookup[item] = index
end

a.sort_by do |item|
  lookup.fetch(item)
end