Thanks! It's exactly what I wanted! This gave me more ideas, so I would like to know if it is also possible to know how many specific cards are in that zone? Thanks again!
Viewing post in How would I do this? (Q&A Thread)
Yes, this is possible using a filter function on the zone's array of Skill IDs for a given party battler. For example,
$gameParty.leader()._cardDeck.filter(x=> x==7).length
will give you the number of Cards in the Party Leader's deck that have the Skill ID 7. You can change the battler, the zone or the specific ID you are looking for to use this expression in multiple ways.