Solution to Sub-task: Group

// Group
function group (mapped_arr) {
    var obj = {}
    mapped_arr.forEach(x => {
        var key = Object.keys(x)[0]; // assign person 
        if (key in obj){
            // push all elements of x[key] into obj[key]
            obj[key].push(Array.from(x[key]));    
        }
        else {
            // Assign copy of the array to the object with key 
            obj[key] = [Array.from(x[key])];
        }
    })
    return obj;
    // return an object {(man,friend): [Friends]}
}
var mapped_arr = [
    { 'AB': [ 'B', 'C', 'D' ] },
    { 'AC': [ 'B', 'C', 'D' ] },
    { 'AD': [ 'B', 'C', 'D' ] },
    { 'AB': [ 'A', 'C', 'D', 'E' ] },
    { 'BC': [ 'A', 'C', 'D', 'E' ] },
    { 'BD': [ 'A', 'C', 'D', 'E' ] },
    { 'BE': [ 'A', 'C', 'D', 'E' ] },
    { 'AC': [ 'A', 'B', 'D', 'E' ] },
    { 'BC': [ 'A', 'B', 'D', 'E' ] },
    { 'CD': [ 'A', 'B', 'D', 'E' ] },
    { 'CE': [ 'A', 'B', 'D', 'E' ] },
    { 'AD': [ 'A', 'B', 'C', 'E' ] },
    { 'BD': [ 'A', 'B', 'C', 'E' ] },
    { 'CD': [ 'A', 'B', 'C', 'E' ] },
    { 'DE': [ 'A', 'B', 'C', 'E' ] },
    { 'BE': [ 'B', 'C', 'D' ] },
    { 'CE': [ 'B', 'C', 'D' ] },
    { 'DE': [ 'B', 'C', 'D' ] } 
];
console.log(group(mapped_arr));