Ruby Multidimensional Array - Remove duplicate in first position, add number in second position -

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for array: 

items = [[60, 3], [60, 3], [276, 2], [276, 2], [48, 2], [207, 2], [46, 2],  [60, 2], [280, 2], [207, 1], [48, 1], [112, 1], [60, 1], [207, 1], [112, 1],  [276, 1], [48, 1], [276, 1], [48, 1], [276, 1], [276, 1], [278, 1], [46, 1],  [48, 1], [279, 1], [207, 1]]

i want combine common numbers in first positions of each sub-array, , add numbers in second positions together.

for instance, you'll see first 4 sub-arrays here are: [60, 3], [60, 3], [276, 2], [276, 2]

this become: [60,6], [276,4] , on.

try this

items.   group_by {|i| i[0]}.   map{|key, value| [key,value.inject(0){|sum, x| sum + x[1]}]}

firstly, use group_by create hash keys first element of each array. have

{  60=>[[60, 3], [60, 3], [60, 2], [60, 1]],  276=>[[276, 2], [276, 2], [276, 1], [276, 1], [276, 1], [276, 1]],  48=>[[48, 2], [48, 1], [48, 1], [48, 1], [48, 1]],  207=>[[207, 2], [207, 1], [207, 1], [207, 1]],  46=>[[46, 2], [46, 1]],  280=>[[280, 2]],  112=>[[112, 1], [112, 1]],  278=>[[278, 1]],  279=>[[279, 1]] }

then create desired result, using map method loop hash. calculate total value each key, using inject method sum second value of each array

[[60, 3], [60, 3], [60, 2], [60, 1]].inject(0) {|sum, x| sum + x[1]} #value 9

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