Swap key with value JSON

Question

I have an extremely large JSON object structured like this:

{A : 1, B : 2, C : 3, D : 4}

I need a function that can swap the values with

Answer 1

A simple TypeScript variant:

const reverseMap = (map: { [key: string]: string }) => {
    return Object.keys(map).reduce((prev, key) => {
        const value = map[key];
        return { ...prev, [value]: [...(prev.value || []), key] };
    }, {} as { [key: string]: [string] })
}

Usage:

const map = { "a":"1", "b":"2", "c":"2" };
const reversedMap = reverseMap(map);
console.log(reversedMap);

Prints: { "1":["a"], "2":["b", "c"] }