• Registered: 2013-02-05
  • Posts: 1

Topic: how to sum the 2 largest elements in an array

I have a method, in which I have created an array of numbers, I want to sum the two largest elements of the array, which I thought worked fine until I moved the numbers around.

def max_2_sums
  array = [3, 4, 5]
  array.sort!
  num_1 = array.max
  num_2 = array.length-1
    max_2_sum = 0
    array.each do |item|
      max_2_sum = num_1 + num_2
    end
    puts max_2_sum
  end

what have I done wrong?

  • jamesw
  • Administrator
  • Offline
  • From: Leeds, UK
  • Registered: 2008-06-07
  • Posts: 2,701

Re: how to sum the 2 largest elements in an array

Try this

def max_2_sums
  array = [1,9,11,2,4,8,32] #The sum of the highest 2values should be 43
  array.sort{ |x, y| y <=> x }
  sum = array[0] + array[1]  
end
What you want and what you need are too often not the same thing!
When your head is hurting from trying to solve a problem, stop standing on it. When you are the right way up you will see the problem differently and you just might find the solution.
(Quote by me 15th July 2009)
  • kham
  • Ticketholder
  • Offline
  • Registered: 2013-03-19
  • Posts: 1

Re: how to sum the 2 largest elements in an array

[1, 3, 2, 5, 3, 6, 34, 4, 2].sort.last(2).reduce(&:+)

and if you need a function

def max_2_sums arr
    arr.sort.last(2).reduce(&:+)
end

max_2_sum [1, 3, 2, 5, 3, 6, 34, 4, 2]

or even

class Array
 def max_2_sums
   self.sort.last(2).reduce(&:+)
end
end

[1,3,54,2,3,5,6].max_2_sums

Last edited by kham (2013-03-20 08:11:34)

  • Registered: 2013-03-18
  • Posts: 20

Re: how to sum the 2 largest elements in an array

Someday I will truly understand bubble sorts (jamesaw's comment) but didn't get em in javascript, still don't get it in ruby - just know they work - which will be important when I'm doing statistics and sorting of averages and such smile

  • Registered: 2013-03-25
  • Posts: 14

Re: how to sum the 2 largest elements in an array

I didn't know about reduce, but I knew about inject:

a.sort.last(2).inject { |sum, i| sum + i }

I tried my very first benchmark on this, too, and happily claim my method to be faster on my machine! smile

#!/usr/bin/env ruby
require 'benchmark'

Benchmark.bm do |b|
  a = [1, 3, 2, 5, 3, 6, 34, 4, 2].sort.last(2)
  
  b.report("inject") do
    1000000.times { a.inject { |sum, i| sum + i } }
  end

  b.report("reduce") do
    1000000.times { a.reduce(&:+) }
  end
end

#       user     system      total        real
# inject  0.800000   0.000000   0.800000 (  0.813485)
# reduce  1.000000   0.000000   1.000000 (  1.015254)