Sum of any two elements in a given array

Question

What's a good way to find sum of any two elements in a given array?

I have the following code, but it looks kind of ugly

def sum_to_n?(a, n)
  sums = []
  a.each_index do |i|
    b = a.drop(i+1)
    b.each_index do |j|
      sums << a[i] + b[j]
    end
  end
end

a method with method? name should return a boolean, it's a convention. — tokland
– tokland, Commented Oct 21, 2013 at 6:19

tokland · Accepted Answer · 2013-10-21 06:15:25Z

1

xs = [1, 5, 8, 10]
xs.combination(2).map { |x, y| x + y }
#=> [6, 9, 11, 13, 15, 18]

answered Oct 21, 2013 at 6:15

tokland

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6 Comments

Sasha Kolsky Over a year ago

Magical! Thanks for quick response. ;)

Patrick Oscity Over a year ago

Or, for the general case xs.combination(n).map {|v| v.reduce(&:+) }

tokland Over a year ago

@p11y: yup, only note that vs.reduce(:+)

Patrick Oscity Over a year ago

@tokland nice! Since when is this possible?

tokland Over a year ago

I think it's possible from 1.8.7, it's well documented. There is a reason why inject allows it: a catamorphism (folding) is usually a binary operation of two values (the accumulated and the element being processed) so it makes sense to get this operator (method). Anyway, I'd also like to have [1,2,3].map(:to_s) :)

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