JavaScript 同步两个数组(对象)/查找增量 [英] JavaScript sync two arrays (of objects) / find delta

问题描述

我有两个数组，旧的和新的，它们在每个位置保存对象.我将如何同步或找到增量(即与旧数组相比，新数组中的新增内容、更新内容和删除内容)

I have two arrays, old and new, which hold objects at each position. How would I sync or find the delta (i.e. what is new, updated and deleted from the new array compared to the old array)

var o = [
    {id:1, title:"title 1", type:"foo"},
    {id:2, title:"title 2", type:"foo"},
    {id:3, title:"title 3", type:"foo"}
];

var n = [
    {id:1, title:"title 1", type:"foo"},
    {id:2, title:"title updated", type:"foo"},
    {id:4, title:"title 4", type:"foo"}
];

根据上面的数据，以id为key，我们会发现id=2的item有一个更新的title，id=3的item被删除了，id=4的item是new.

With the above data, using id as the key, we'd find that item with id=2 has an updated title, item with id=3 is deleted, and item with id=4 is new.

是否有现有的库具有有用的功能，或者是循环和内循环的情况，比较每一行..e.g.

Is there an existing library out there that has useful functions, or is it a case of loop and inner loop, compare each row..e.g.

for(var i=0, l=o.length; i<l; i++)
{   
    for(var x=0, ln=n.length; x<ln; x++)
    {
        //compare when o[i].id == n[x].id    
    }  
}

这种比较三遍，找新的、更新的、删除的?

Do this kind of comparison three times, to find new, updated and deleted?

推荐答案

做你需要的事情没有什么神奇的.您需要遍历两个对象以查找更改.一个很好的建议是将您的结构转换为地图以加快搜索速度.

There's no magic to do what you need. You need to iterate through both objects looking for changes. A good suggestion is to turn your structure into maps for faster searches.

/**
 * Creates a map out of an array be choosing what property to key by
 * @param {object[]} array Array that will be converted into a map
 * @param {string} prop Name of property to key by
 * @return {object} The mapped array. Example:
 *     mapFromArray([{a:1,b:2}, {a:3,b:4}], 'a')
 *     returns {1: {a:1,b:2}, 3: {a:3,b:4}}
 */
function mapFromArray(array, prop) {
    var map = {};
    for (var i=0; i < array.length; i++) {
        map[ array[i][prop] ] = array[i];
    }
    return map;
}

function isEqual(a, b) {
    return a.title === b.title && a.type === b.type;
}

/**
 * @param {object[]} o old array of objects
 * @param {object[]} n new array of objects
 * @param {object} An object with changes
 */
function getDelta(o, n, comparator)  {
    var delta = {
        added: [],
        deleted: [],
        changed: []
    };
    var mapO = mapFromArray(o, 'id');
    var mapN = mapFromArray(n, 'id');    
    for (var id in mapO) {
        if (!mapN.hasOwnProperty(id)) {
            delta.deleted.push(mapO[id]);
        } else if (!comparator(mapN[id], mapO[id])){
            delta.changed.push(mapN[id]);
        }
    }

    for (var id in mapN) {
        if (!mapO.hasOwnProperty(id)) {
            delta.added.push( mapN[id] )
        }
    }
    return delta;
}

// Call it like
var delta = getDelta(o,n, isEqual);

示例见http://jsfiddle.net/wjdZ6/1/

这篇关于JavaScript 同步两个数组(对象)/查找增量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！