Ruby - pushing values from an array combination to a new array

Question

I am trying to print all the different sums of all combinations in this array [1,2,3]. I want to first push every sum result to a new array b, then print them using b.uniq so that non of the sum results are repeated. However, with the code I have, the 3 repeats itself, and I think it is because of the way it is pushed into the array b.

Is there a better way of doing this?

a = [1,2,3]
b = []

b.push a

b.push a.combination(2).collect {|a,b| (a+b)}

b.push a.combination(3).collect {|a,b,c| (a+b+c)}

puts b.uniq
p b #[[1, 2, 3], [3, 4, 5], [6]]

Can someone please help me with this? I am still new in ruby.

But the first 3 you see, it's not a result of a sum operation. — Sergio Tulentsev
– Sergio Tulentsev, Commented Oct 26, 2015 at 13:12

Drenmi · Accepted Answer · 2015-10-26 13:53:14Z

Because an Array of arbitrary length can be summed using inject(:+), we can create a more general solution by iterating over the range 1..n, where n is the length of the Array.

(1..(a.size)).flat_map do |n|
  a.combination(n).map { |c| c.inject(&:+) }
end.uniq
#=> [1, 2, 3, 4, 5, 6]

By using flat_map, we can avoid getting the nested Array result, and can call uniq directly on it. Another option to ensure uniqueness would be to pass the result to a Set, for which Ruby guarantees uniqueness internally.

require "set"

sums = (1..(a.size)).flat_map do |n|
  a.combination(n).map { |c| c.inject(&:+) }
end

Set.new(sums)
#=> #<Set: {1, 2, 3, 4, 5, 6}>

This will work for an any Array, as long as all elements are Fixnum.

Jeremy B. · Accepted Answer · 2015-10-26 12:53:40Z

0

If all you want is an array of the possible sums, flatten the array before getting the unique values.

puts b.flatten.uniq

What is happening is uniq is running over a multi-dimensional array. This causes it to look for duplicate arrays in your array. You'll need the array to be flattened first.

answered Oct 26, 2015 at 12:53

Jeremy B.

9,2323 gold badges48 silver badges57 bronze badges

Collectives™ on Stack Overflow

Ruby - pushing values from an array combination to a new array

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related