From: Rob Biedenharn <Rob@...>
Date: 2011-01-15T09:14:37+09:00
Subject: Re: array dynamic intersection and union

On Jan 14, 2011, at 5:39 PM, Jamal Soueidan wrote:

> Hello Rob,
>
> Sorry I did not explain myself first time.
>
> But I let us say I have these hashes.
>
> rule = {:array => [1,2,3,4], :condition => "AND"}
> rule2 = {:array => [1,2,3,4], :condition => "OR"}
> rule3 =  {:array => [3,4]}
>
> How can I intersection and union based on the conditions in the hash
> through them all?
>
> So it end up like this
>
> array = rule[:array] & rule2[:array] | rule3[:array]

Let me rephrase that because you still aren't giving enough  
information to really know what you're trying to do.

Given an array of hashes:
input = [ {:array => [1,2,3,4], :condition => "AND"},
           {:array => [2,4,6,8], :condition => "OR"},
           {:array => [1,3]},
         ]
array = input[0][:array] & input[1][:array] | input[2][:array]
=> [2, 4, 1, 3]


Well, if you apply the operations serially, you will actually get  
something like:

array = ((input[0][:array] & input[1][:array]) | input[2][:array])

Since & is higher precendence than |, the answer is the same, but if  
you change the order:

array =   input[0][:array] | input[1][:array]  & input[2][:array]
=> [1, 2, 3, 4]

is not the same as:

array = ((input[0][:array] | input[1][:array]) & input[2][:array])
=> [1, 3]


def combine(arrays)
   result, op = [], "OR"
   arrays.each do |hsh|
     case op
     when "OR"
       result |= hsh[:array]
     when "AND"
       result &= hsh[:array]
     end
     op = hsh[:condition]
   end
   result
end

combine(input)
#=> [2, 4, 1, 3]

-Rob

Rob Biedenharn		
Rob@AgileConsultingLLC.com	http://AgileConsultingLLC.com/
rab@GaslightSoftware.com		http://GaslightSoftware.com/