Question

@data, @x, @y, and @z are all arrays of the same type. I use @data in my view to iterate through it and display all the values.

  @data = if params[:a] == "1"
    @x
  elsif params[:b] == "1"
    @y 
  elsif params[:c] == "1"
    @z

What I’d like to do is also intersect the arrays if multiple parameters are applied. So, for example, if ?a=1&b=2 is appended to the URL, then I’d like @data to equal @x & @y

I’m not sure how to write this code – what’s the easiest way to figure out which params == 1 and then intersect the corresponding arrays and store that in @data?

Answer 1

Fortunately, Ruby makes this easy!

@data = [params[:a] && @x, params[:b] && @y, params[:c] && @z].compact.inject(:&)

This constructs an array of either arrays (if the parameter is present; you could check == '1' if you wanted to be more specific) or nils (if it is not present). compact then strips the nils out of the array, and we can then intersect the remaining values by calling inject(:&).

The inject call iterates over your array of values, takes the first value, and then applies the & method with the next value as a parameter. It then takes the result and applies & with the third parameter, and so on, resulting in a final value which is the intersection of all of the arrays in the passed array.