How to dynamically select and set an app variable

Hi all,

In my app I have an app variable called deck_mames = ["a","b","c",...,"i"] which hold the names of nine decks. I have another variable called cards_in_deck, which is an object with 9 properties, each property being a list of text holding the card IDs containing in each deck:

{
“decks”: {
“a”: [“cardID1”,“cardID2”,…,“cardIDn”],
“b”: [“cardID12”,“cardID13”,…,“cardIDn”],
.
.
.
“i”: [“cardID92”,“cardID93”,…,“cardIDn”]
}
}

Depending on the decision the user takes, I need to take, a cardID from a deck x and move it to a deck z, x and z being any of "a", "b", "c"...., "i".

Question: how to use the list deck_names to select deck x and deck z in cards_in_deck, and assign a new value to only these two properties?