Created
January 1, 2014 15:19
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| // Frees the `[].slice` method to accept `this` as the first actual argument, | |
| // rather than a special argument. | |
| var toArray = Function.call.bind([].slice) | |
| // To make searching efficient (O(1)), we switch the | |
| // list of things to a HashMap, which allows we to | |
| // retrieve an item by its name in constant time. | |
| function indexBy(field, list) { | |
| return list.reduce(function(result, item) { | |
| result[item[field]] = item | |
| return result | |
| }, {}) | |
| } | |
| // Finally, we want something that for every item in | |
| // the input array, enriches the object with the information | |
| // from the other array | |
| function mergeOn(hashmap, field, list) { | |
| return list.reduce(function(result, item) { | |
| var key = item[field] | |
| return key in hashmap? push(result, extend(hashmap[key], item)) | |
| : /* otherwise */ result | |
| }, []) | |
| function push(xs, x){ xs.push(x); return xs } | |
| } | |
| // This just merges a list of objects | |
| function extend(/* ...objects */) { | |
| return toArray(arguments).reduce(function(result, source) { | |
| return Object.keys(source).reduce(function(result, key) { | |
| result[key] = source[key] | |
| return result | |
| }, result) | |
| }, {}) | |
| } | |
| // Test | |
| var arr1 = [ | |
| { id: 1, parentId: 34}, | |
| { id: 2, parentId: 35} | |
| ]; | |
| var arr2 = [ | |
| { id: 34, text: "foo" }, | |
| { id: 35, text: "bar" }, | |
| { id: 36 } | |
| ] | |
| mergeOn(indexBy('id', arr2), 'parentId', arr1) | |
| // => [ | |
| // { id: 1, parentId: 34, text: "foo" }, | |
| // { id: 2, parentId: 35, text: "bar" } | |
| // ] |
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