Needing to find matches in my controller from an array! Ruby on Rails

Question

I am in a broken spot. I was able to get the array from into @set1 and now need to compare @set1 with @set2 and see how many matches there are. I can get the @array1 to work correctly if I have static numbers in an array in @array2 but not when I make it dynamic.

I need a way to compare these two arrays and am at a loss now!

def show
  @set1 = Set1.find(params[:id])
  @set2 = Set2.where(:date => @set1.date)

  @array1 = [Set1.find(params[:id]).let1, Set1.find(params[:id]).let2]
  @array2 = [Winnings.where(:date => @set1.date).let1, Winnings.where(:date => @set1.date).let2]
  @intersection = @array1 & @array2
end

Found the starting point at: http://stackoverflow.com/questions/5013880/ruby-compare-2-arrays-for-matches-and-count-the-number-of-match-instances — nathanielelliott, Nov 23 '13 at 04:56
http://stackoverflow.com/questions/19107761/activerecord-find-and-only-return-selected-columns-aligned-with-id — nathanielelliott, Nov 23 '13 at 05:00

score 0 · Accepted Answer · answered Nov 23 '13 at 18:12

I think part of the problem here is that you can make new objects with the same attributes but that do not respond properly to the comparisons that the intersection operator :& uses.

Example:

class Thing
  attr_reader :first,:last
  def initialize(first,last)
    @first = first
    @last = last
  end
end

thing1 = Thing.new("John","Smith")
thing2 = Thing.new("John","Smith")

thing1 == thing2
# => false

[thing1] & [thing2]
# => []

You might consider mapping each array to some identifying value (maybe id) and finding the intersection of those arrays. That is to say

@set1 = Set1.find(params[:id])
@set2 = Set2.where(:date => @set1.date)

@array1 = [Set1.find(params[:id]).let1, Set1.find(params[:id]).let2]
@array2 = [Winnings.where(:date => @set1.date).let1, Winnings.where(:date => @set1.date).let2]

@array1.map{|obj| obj.id} & @array2.map{|obj| obj.id}
# => an array of unique object ids that are in both @array1 and @array2

Or, if you want the objects themselves...

(@array1.map{|obj| obj.id} & @array2.map{|obj| obj.id}).map{ |id| Set.find(id) }

Just wanted to say that this worked like a charm. Thank you for your assistance, it lead me right to what I needed to do! — nathanielelliott, Dec 12 '13 at 16:20

Needing to find matches in my controller from an array! Ruby on Rails

1 Answers1