How can I sum array elements in place in ruby?

Question

How can I create a new array for summing array elements in place in Ruby?

[1,2,3,4,5].each_cons(2).map {|a, b| a + b }

gives me [3, 5, 7,

Answer 1

[1, 2, 3, 4, 5].each_with_object([]){|e, a| a.push(a.last.to_i + e)}
# => [1, 3, 6, 10, 15]

Answer 2

Another variation:

> [1, 2, 3, 4, 5].reduce([]) {|acc, el| acc << el + (acc[-1] || 0); acc}
#=> [1, 3, 6, 10, 15]

Yuk.

Answer 3

Lots of ways to do this. One way is to create an Enumerator instance and use inject:

def adder array
  enum = Enumerator.new do |y|
    array.inject (0) do |sum, n|
      y << sum + n
      sum + n
    end
  end
  enum.take array.size
end

adder [1,2,3,4,5] #=> [1, 3, 6, 10, 15]

Answer 4

More simple for understanding, I think:

temp_sum = 0
arr.map! {|e| temp_sum += e }
=> [1, 3, 6, 10, 15]

If you want to create a new array instead of existing one, just use map instead of map!

Answer 5

It's not very elegant, but it seems to work :

[1,2,3,4,5].each_with_object([]){|i,l| l<<(l.last||0)+i}
#=> [1,3,6,10,15]