ruby: sum corresponding members of two or more arrays

Question

I\'ve got two (or more) arrays with 12 integers in each (corresponding to values for each month). All I want is to add them together so that I\'ve got a single array with su

Answer 1

@FriendFX, you are correct about @user2061694 answer. It only worked in Rails environment for me. You can make it run in plain Ruby if you make the following changes...

In the IRB

[[0, 0, 0], [2, 2, 1], [1,3,4]].transpose.map {|a| a.inject(:+)}
 => [3, 5, 5]


[[1,2,3],[4,5,6]].transpose.map {|a| a.inject(:+)}
 => [5, 7, 9]

Answer 2

here's my attempt at code-golfing this thing:

// ruby 1.9 syntax, too bad they didn't add a sum() function afaik
[1,2,3].zip([4,5,6]).map {|a| a.inject(:+)} # [5,7,9]

zip returns [1,4], [2,5], [3,6], and map sums each sub-array.

Answer 3

This might not be the best answer but it works.

array_one = [1,2,3]
array_two = [4,5,6]
x = 0
array_three = []
while x < array_one.length
  array_three[x] = array_one[x] + array_two[x]
  x += 1
end

=>[5,7,9]

This might be more lines of code than other answers, but it is an answer nonetheless

Answer 4

[[1,2,3],[4,5,6]].transpose.map{|a| a.sum} #=> [5,7,9]

Answer 5

For:

a = [1,2,3]
b = [4,5,6]

You could zip and then use reduce:

p a.zip(b).map{|v| v.reduce(:+) }
#=> [5, 7, 9]

Or, if you're sure that array a and b will always be of equal length:

p a.map.with_index { |v, i| v + b[i] }
#=> [5, 7, 9]

Answer 6

Here's the transpose version Anurag suggested:

[[1,2,3], [4,5,6]].transpose.map {|x| x.reduce(:+)}

This will work with any number of component arrays. reduce and inject are synonyms, but reduce seems to me to more clearly communicate the code's intent here...