Comparing & sorting array of hashes in Ruby

Question

I have two arrays. They have different attributes.

array1 = [{name: "apple", quantity: 2}, {name: "grape", quantity: 10}, {name: "pear", quantity: 3}]
array2 = [{name: "grape", freshness: 9}, {name: "apple", freshness: 7}, {name: "pear", freshness: 10}]

I would like to sort array1 based on array2's order, by name. The result would be:

array1 = [{name: "grape", quantity: 10}, {name: "apple", quantity: 2}, {name: "pear", quantity: 3}]

Answer 1

You could build a name => index hash:

h = array2.map { |e| e[:name] }.each_with_index.to_h
#=> {"grape"=>0, "apple"=>1, "pear"=>2}

And sort by that hash:

array1.sort_by { |e| h[e[:name]] }
#=> [{:name=>"grape", :quantity=>10}, {:name=>"apple", :quantity=>2}, {:name=>"pear", :quantity=>3}]

Answer 2

Here's a simple way to do it given your current data structure.

array1 = array1.sort_by { |x| array2.find_index { |y| y[:name] == x[:name] } }

However, note that find_index takes O(n) time. This can be improved by using a different model for your data or by doing some preprocessing (e.g., see Stefan's answer).