What's the efficient way to multiply two arrays and get sum of multiplied values in Ruby?

Question

What\'s the efficient way to multiply two arrays and get sum of multiply values in Ruby? I have two arrays in Ruby:

array_A = [1, 2, 1, 4, 5, 3, 2, 6, 5, 8, 9]
a         


        

Answer 1

Try the NMatrix gem. It is a numerical computation library. I think it uses the same C and C++ libraries that Octave and Matlab uses.

You would be able to do the matrix multiplication like this:

require 'nmatrix'

array_A = [1, 2, 1, 4, 5, 3, 2, 6, 5, 8, 9]
array_B = [3, 2, 4, 2, 5, 1, 3, 3, 7, 5, 4]

vec_a = array_A.to_nm([1,array_A.length])    # create an NMatrix
vec_b = array_B.to_nm([1,array_B.length])

sum = vec_a.dot(vec_b.transpose)

I am not sure how the speed will compare using pure Ruby but I imagine it to be faster, especially for large and sparse vectors.

Answer 2

array1.zip(array2).map{|x| x.inject(&:*)}.sum

Answer 3

I would start simple and use the Ruby matrix class:

require 'matrix'

a = Matrix.row_vector( [1, 2, 1, 4, 5, 3, 2, 6, 5, 8, 9])
b = Matrix.column_vector([3, 2, 4, 2, 5, 1, 3, 3, 7, 5, 4])

result= a * b
puts result.element(0,0)

If this turns out to be too slow, then do the exact same method but with an external math library.