如何对数组中数组的每个唯一元素求和

Question

I have an array like:

[1, 84]
[11, 29]
[11, 84]
[12, 18]
[15, 55]
[15, 4]

I Want to generate a new array from this array like:

[1, 84, 1]
[11, 113, 2]
[12, 18, 1]
[15, 59, 2]

where the first element of the each sub-array will be unique and their corresponding second element will be sum, and the third element will be their count. In case of 11 , 29 + 84 = 113 , and 11 exists 2 times, so [11, 113, 2] .

Answer 1

a.group_by(&:first).map { |k,v| [k,v.map(&:last).inject(:+),v.size] }
# => [[1, 84, 1], [11, 113, 2], [12, 18, 1], [15, 59, 2]]

Answer 2

a = [
  [1, 84],
  [11, 29],
  [11, 84],
  [12, 18],
  [15, 55],
  [15, 4]
]

a.group_by(&:first).values.map {|arys| [arys.first.first, arys.map{|a| a[1]}.inject(:+), arys.count]}