How to Sum Values of Identical Keys in an Array of JavaScript Objects?

Summing Values of Similar Keys in an Array of Objects

Problem:

Given an array of objects, determine a method to compute the sum (or other mathematical operations) of values associated with objects that share the same key.

Example:

Consider the following array of objects:

[
    {
        'name': 'P1',
        'value': 150
    },
    {
        'name': 'P1',
        'value': 150
    },
    {
        'name': 'P2',
        'value': 200
    },
    {
        'name': 'P3',
        'value': 450
    }
]

The desired output would sum the 'value' property for objects with matching 'name' properties, resulting in:

[
    {
        'name': 'P1',
        'value': 300
    },
    {
        'name': 'P2',
        'value': 200
    },
    {
        'name': 'P3',
        'value': 450
    }
]

Solution:

The solution involves iterating through the input array, aggregating identical key values into a separate object.

var obj = [
    { 'name': 'P1', 'value': 150 },
    { 'name': 'P1', 'value': 150 },
    { 'name': 'P2', 'value': 200 },
    { 'name': 'P3', 'value': 450 }
];

var holder = {};

obj.forEach(function(d) {
  if (holder.hasOwnProperty(d.name)) {
    holder[d.name] = holder[d.name] + d.value;
  } else {
    holder[d.name] = d.value;
  }
});

The resulting holder object will contain key-value pairs where the keys are unique name values, and the values are the sum of associated value properties.

{
  'P1': 300,
  'P2': 200,
  'P3': 450
}

To generate the desired output, iterate through the properties of the holder object and create new objects:

var obj2 = [];

for (var prop in holder) {
  obj2.push({ name: prop, value: holder[prop] });
}

The final result, stored in obj2, fulfills the requirements of summing values for objects with similar keys.

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