Question

I need to make intersection of n-arrays with millions of elements (database ID’s).
This code works perfect, but slow (with very big arrays). How can i improve it?

[[1,2,3,4],[2,4,6,8],[4,5,8]].inject([]){|c,v| c = v if c.size==0; c = c&v if c.size>0; c }

Answer 1

Ruby provides an intersection opperator.

May I suggest you try this:

> [[1,2,3,4],[2,4,6,8],[4,5,8]].reduce{ |accum, arr| accum & arr }
=> [4] 

Edit:

This can be written a little more concise but it suffers from readability.

[[1,2,3,4],[2,4,6,8],[4,5,8]].reduce(:&)