JavaScript sync two arrays (of objects) / find delta

问题

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"}
];

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.

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    
    }  
}

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

回答1:

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);

See http://jsfiddle.net/wjdZ6/1/ for an example

回答2:

This is typescript version of @Juan Mendes answer

  mapFromArray(array: Array<any>, prop: string): { [index: number]: any } {
    const map = {};
    for (let i = 0; i < array.length; i++) {
      map[array[i][prop]] = array[i];
    }
    return map;
  }

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

  getDelta(o: Array<any>, n: Array<any>, comparator: (a, b) => boolean): { added: Array<any>, deleted: Array<any>, changed: Array<any> } {
    const delta = {
      added: [],
      deleted: [],
      changed: []
    };
    const mapO = this.mapFromArray(o, 'id');
    const mapN = this.mapFromArray(n, 'id');
    for (const 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 (const id in mapN) {
      if (!mapO.hasOwnProperty(id)) {
        delta.added.push(mapN[id]);
      }
    }
    return delta;
  }

来源：https://stackoverflow.com/questions/14966207/javascript-sync-two-arrays-of-objects-find-delta

标签

javascript

sync