Question

Given the following simple data set, what is the best way to average the values for the sets 0 25 53 and 80.

  [["0", "148.5"],
   ["0", "146.5"],
   ["0", "148.6"],
   ["0", "202.3"],
   ["25", "145.7"],
   ["25", "145.5"],
   ["25", "147.4"],
   ["25", "147.3"],
   ["53", "150.4"],
   ["53", "147.6"],
   ["53", "147.8"],
   ["53", "215.4"],
   ["80", "150.4"],
   ["80", "149.4"],
   ["80", "148.0"],
   ["80", "149.9"]]

Answer 1

It’s simple enough with inject. I often implement a general group_by method in projects to help with stuff like this.

If data is large and performance matters consider using a numeric library or database if appropriate.

data = [ ... ]

groups = data.inject({}) do |hash, pair| 
  hash[pair.first] ||= []
  hash[pair.first] << pair.last.to_f
  hash
end

groups.inject({}) do |hash, pair| 
  hash[pair.first] = pair.last.inject(0,&:+) / pair.last.size
  hash
end