CODEWITHSUNDEEP
ruby-on-railsrubyarrays
Anh
Anh

Reputation: 27

Ruby on Rails - Get max and sum group by multiple keys in array at same time

Having array:

[ { 'a' => 1, 'b' => 1, 'c' =>  1, 'd' => 1, 'e' => 2},
  { 'a' => 1, 'b' => 1, 'c' =>  2, 'd' => 1, 'e' => 2},
  { 'a' => 1, 'b' => 1, 'c' =>  3, 'd' => 1, 'e' => 2},
  { 'a' => 1, 'b' => 2, 'c' =>  4, 'd' => 2, 'e' => 2 },
  { 'a' => 1, 'b' => 2, 'c' =>  5, 'd' => 2, 'e' => 2 },
  { 'a' => 2, 'b' => 1, 'c' =>  6, 'd' => 3, 'e' => 2 },
  { 'a' => 2, 'b' => 1, 'c' =>  7, 'd' => 3, 'e' => 2 },
  { 'a' => 2, 'b' => 1, 'c' =>  8, 'd' => 3, 'e' => 2 },
  { 'a' => 2, 'b' => 2, 'c' =>  9, 'd' => 4, 'e' => 2 },
  { 'a' => 2, 'b' => 2, 'c' => 10, 'd' => 4, 'e' => 2 } ]

I want to get max of 'c', sum 'd', sum 'e' grouped by 'a' and 'b'.

So, the result should be:

[ { 'a' => 1, 'b' => 1, 'c' =>  3, 'd' => 3, 'e' => 6},
  { 'a' => 1, 'b' => 2, 'c' =>  5, 'd' => 4, 'e' => 4},
  { 'a' => 2, 'b' => 1, 'c' =>  8, 'd' => 9, 'e' => 6},
  { 'a' => 2, 'b' => 2, 'c' => 10, 'd' => 8, 'e' => 4} ]

So far, I follow How to find max value grouped by multiple keys in array of hashes?, using this code to get max of each group

a.group_by { |h| h.values_at("a", "b") }.map { |_, v| v.max_by { |h| h["c"] } }

Please guide me, get sum too. Thanks a lot.

P/s: using Ruby 1.8.7 and Rails 2.3.5

Upvotes: 0

Views: 564

Answers (2)

Max Hollmann
Max Hollmann

Reputation: 345

This works:

a.group_by { |h| h.values_at("a", "b") }.map do |_, v|
  v.inject { |c, h| c.merge({ "c" => [c["c"], h["c"]].max,
                              "d" => c["d"] + h["d"],
                              "e" => c["e"] + h["e"] }) }
end

Upvotes: 1

Jonathan
Jonathan

Reputation: 6537

As you requested in the comments, here's my comment extended into an easier format. My edit to Max's post was rejected. 

a.group_by { |h| h.values_at("a", "b") }.
  map { |_, v| v.max_by { |h| h["c"] }.
    tap { |h| h["d"] = v.inject(0) { |sum, h| sum + h["d"] } }.
    tap { |h| h["e"] = v.inject(0) { |sum, h| sum + h["e"] } } }

Upvotes: 1

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