How can I decrease a key of a state in React without knowing the key name? [duplicate]

I have the following state in React:

const [counter, setCounter] = useState({foo: 1, bar: 1});

and I have data like

const data = [{who: "foo", otherVal: "bla"}, {who: "bar", otherVal: "bla"}];

If I remove an object from the data array, I want to decrease the counter by 1 related to the who value of the deleted object.

If {who: "foo", otherVal: "bla"} gets removed, I want to decrease the foo key of the counter because who === "foo". But In my app I don’t know that foo is foo or bar is bar. I must use counter[data.who] somehow to update my state.