Sum of specific values grouped by other values inside an array

Question

I have this array structure in which at $arr[5]index I have a value that represents a number of occurrences for each object of my array $arr:

$arr=[
  [
    "some_value",
    "some_value",
    "cluster_0",
    "area_2",
    "some_value",
    "1"
  ],
  [
    "some_value",
    "some_value",
    "cluster_0",
    "area_2",
    "some_value",
    "2"
  ],
  [
    "some_value",
    "some_value",
    "cluster_0",
    "area_3",
    "some_value",
    "1"
  ],
  [
    "some_value",
    "some_value",
    "cluster_1",
    "area_3",
    "some_value",
    "3"
  ],
  [
    "some_value",
    "some_value",
    "cluster_1",
    "area_4",
    "some_value",
    "2"
  ],
  [
    "some_value",
    "some_value",
    "cluster_1",
    "area_4",
    "some_value",
    "2"
  ]
];

What I'm trying to obtain is to sum each of those$arr[5] values grouping by $arr[2](the cluster) and the $arr[3](the area).

Here's the expected output

$res=[
  [
    "cluster_0",
    "area_2",
    3
  ],
  [
    "cluster_0",
    "area_3",
    1
  ],
  [
    "cluster_1",
    "area_3",
    3
  ],
  [
    "cluster_1",
    "area_4",
    4
  ]
];

As you can see I have the sum of that specific value according to area and cluster matching. Is there any good approach in javascript for perform this kind of operation? I thought about a simple for loop and inside the loop an if condition for sum just the value that share the same $arr[2](the cluster) and the $arr[3](the area) values.

Nina Scholz · Accepted Answer · 2017-11-13 22:27:22Z

You could take the indices for the groups and the value index and generate a new result set with using the group as hash key. Then add the value to the group.

function groupBy(array, groups, value) {
    var result = [],
        hash = Object.create(null);

    array.forEach(function (a) {
        var keys = groups.map(function (i) { return a[i] }),
            key = keys.join('|');
        if (!hash[key]) {
            hash[key] = keys.concat(0);
            result.push(hash[key]);
        }
        hash[key][hash[key].length - 1] += +a[value];
    });
    return result;
}

var array = [["some_value", "some_value", "cluster_0", "area_2", "some_value", "1"], ["some_value", "some_value", "cluster_0", "area_2", "some_value", "2"], ["some_value", "some_value", "cluster_0", "area_3", "some_value", "1"], ["some_value", "some_value", "cluster_1", "area_3", "some_value", "3"], ["some_value", "some_value", "cluster_1", "area_4", "some_value", "2"], ["some_value", "some_value", "cluster_1", "area_4", "some_value", "2"]],
    result = groupBy(array, [2, 3], 5);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Telman · Accepted Answer · 2017-11-13 22:54:23Z

Consider also this solution,

var data = $arr.reduce(function(acc, item) {
  var clusterName = item[2],
      areaName = item[3];
  acc[clusterName] = acc[clusterName] || {};
  acc[clusterName][areaName] = acc[clusterName][areaName] || 0;
  acc[clusterName][areaName] += parseInt(item[5]);
  return acc;
}, {});

console.log(data);

var array = Object.keys(data).reduce(function(acc, clusterItem) {
  Object.keys(data[clusterItem]).forEach(function(areaItem) {
    var item = [];
    item.push(clusterItem);
    item.push(areaItem);
    item.push(data[clusterItem][areaItem]);
    acc.push(item);
  });
  return acc;
}, []);

console.log(array);

Here at the first step all the items are calculated and added to the object. The second one converts the object to the required structure (array).

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Sum of specific values grouped by other values inside an array

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