Sum javascript object propertyA values with same object propertyB in array of objects

Question

How would one take a javascript array of objects such as:

my objArr = [
{key:Mon Sep 23 2013 00:00:00 GMT-0400, val:42},
{key:Mon Sep 24 2013 00:00:00 GMT-04         


        

Answer 1

Recently l needed a similar implementation and l used a similar solution offered by some guy that used reduce function. Few days later i wanted to implement something similar by myself and here is the result.

const users = [
        { id: 1, name: 'ernest', spent: 40 }, 
        { id: 2, name: 'ernest', spent: 40 },
        { id: 3, name: 'astrit', spent: 22 },
        { id: 4, name: 'astrit', spent: 2956 },
        { id: 5, name: 'astrit', spent: 22 }, 
        { id: 6, name: 'besart', spent: 40 }, 
        { id: 7, name: 'besart', spent: 100}, 
        { id: 8, name: 'besart', spent: 4000 }
    ];

        const sum = [];

        users.forEach(el => {
            if(sum.length === 0){
                delete el.id;
                sum.push(el);
            }    
            else
            {
                const get = () => {
                    for(let i = 0; i < sum.length; i++){
                        if(sum[i].name === el.name ){
                            return { stat: true, id: i };
                        }
                    }
                }

                let i = get();
                if(i){
                    sum[i.id].spent += el.spent;
                }
                else
                {
                    delete el.id;
                    sum.push(el);
                }
            }
        });

        console.log(sum);

Output:

[ { name: 'ernest', spent: 80 }, { name: 'astrit', spent: 3000 }, { name: 'besart', spent: 4140 } ]