将JavaScript数组中的对象合并为对象

Question

I am trying to create a single JavaScript object from an array of objects.

Some values in the object remain the same, while the numerical or float values need to be summed up to form the new single object.

How can this be achieved?

[{
    'visit_date': '2013-02-02',
    'house_number': '22',
    'price': 12.98,
    'count_value': 21.554,
    'variance': -23.434343434
},
{
    'visit_date': '2013-02-02',
    'house_number': '22',
    'price': 34.78,
    'count_value': 1.34,
    'variance': -23.434343434
},
{
    'visit_date': '2013-02-02',
    'house_number': '22',
    'price': 61.41,
    'count_value':1.94,
    'variance': -12.977677874
}]

Answer 1

Loop through the array, use a for-in loop on each object, and for entries where typeof value === "number" , sum them up. Presumably do something useful when they aren't numbers, but you haven't said what. :-)

Sorry, missed the jQuery tag. It can be shorter with jQuery's each :

var dest = {};

$.each(source, function(index, entry) {
    $.each(entry, function(key, value) {
        if (typeof value === "number") {
            dest[key] = key in dest ? dest[key] + value : value;
        }
        else {
            // do something useful with non-numbers
        }
     });
});

each will loop through the array elements if you give it an array, or through the properties of an object if you give it a non-array object. So in the above, the outer each loops through your array, and the inner each loops through each object's properties.

The in operator on this line:

dest[key] = key in dest ? dest[key] + value : value;

...tells us whether dest already has a key with that name: If so, we add the value to it. If not, we create a new property for that key using the value.

---

Original non-jQuery:

Roughly :

var dest = {};
var entry;
var index;
var key;
var value;

for (index = 0; index < source.length; ++index) {
    entry = source[index];
    for (key in entry) {
        value = entry[key];
        if (typeof value === "number") {
            dest[key] = key in dest ? dest[key] + value : value;
        }
        else {
            // do something useful with non-numbers
        }
    }
}

Answer 2

You can use the reduce function to achieve it

var result = a.reduce(function (acc, c) {
    acc.visit_date = c.visit_date;
    acc.house_number = c.house_number;
    acc.price += c.price;
    acc.count_value += c.count_value;
    acc.variance += c.variance;
    return acc;
}, {
    'visit_date': '',
    'house_number': '',
    'price': 0,
    'count_value': 0,
    'variance': 0
});

The result will be

{
    visit_date: "2013-02-02",
    house_number: "22",
    price: 109.17,
    count_value: 24.834,
    variance: -59.846364742
}

Answer 3

Something like this perhaps? http://jsfiddle.net/tQLy5/1/

function aToObject(a) {
    var o = {}, l = a.length;
    while (l--) {
        for (key in a[l]) {
            if (o.hasOwnProperty(key) && typeof (o[key]) === 'number') {
                o[key] += a[l][key];   
            } else {
                 o[key] = a[l][key];   
            }
        }
    }
    return o;
}

Just iterate over the whole array and then over the properties of the objects in array. If the property is number you add them together, otherwise you just assign the property to the new object.