Question

I have to find intersection elements of 3 integer arrays
say a, b, c with a condition; if any of the array is null ( [] ),
simply ignore the array and find intersection of the remaining arrays,
and if all three are null, then return [].
Thanks in advance.

ps:Ruby 1.9.3

Answer 1

One way to do it would be this:

[ a, b, c ].tap{ |a| a.delete( [] ) }.reduce( :& ) || []

Other options suggested in the discussion are:

[ a, b, c ].reject( &:empty? ).reduce( :& ) || []

and:

[ a, b, c ].select( &:any? ).reduce( :& ) || []

But in this last case, beware of non-empty arrays with explicit nil elements, such as [ nil ], cause they still fail #any? test.