Reduce an array of objects and sum property for each distinct object

Question

I am not sure for what functions I should look at to achieve what I am trying to do. Probably reduce is not correct.

A database query returns a list of objects like this

Answer 1

First function reduces result to find the sums for each group.

Then we go through each group to return the results.

var result = [{group1: 'A', group2: 'A', SUM: 5},
  {group1: 'A', group2: 'B', SUM: 2},
  {group1: 'C', group2: 'B', SUM: 3}
];

(function groupSum(result) {
  var sums = result.reduce(function(a, e) {
    a.group1_SUM[e.group1] = (a.group1_SUM[e.group1] || 0) + e.SUM;
    a.group2_SUM[e.group2] = (a.group2_SUM[e.group2] || 0) + e.SUM;
    return a;
  }, {group1_SUM: {}, group2_SUM: {}});

  return Array.from(new Set(Object.keys(sums.group1_SUM).concat(Object.keys(sums.group2_SUM)))).map(function(e) {
    return {
      groupName: e, group1_SUM: sums.group1_SUM[e] || 0, group2_SUM: sums.group2_SUM[e] || 0
    }
  });
})(result);