Question

[[1, 20],[2,30],[1,5],[4,5]]

In ruby how does one go through this array and add the second element if the first is the same with and output such as:

[[1, 25],[2,30],[4,5]]

Answer 1

If order isn’t important, inserting the pairs into a hash, adding if the key already exists, and then flattening the hash back into an array is a neat way. In irb:

>> a = [[1, 20],[2,30],[1,5],[4,5]]

=> [[1, 20], [2, 30], [1, 5], [4, 5]]

>> a.inject(Hash.new(0)) { |h, p| h[p[0]] += p[1]; h }.to_a

=> [[1, 25], [2, 30], [4, 5]]