You have the "application" XML (the left side) and the event XML (the right side) in your comparison.

You will need a hash to know whether an element is in the application XML array.

For that, you initialize the hash using the application id as key and (say) the hash reference from the right side as the value.

Then, for each event in the event array, you look in the application ID hash for the application id. If it exists, you have found a match.