## 問題 Problem 你有一個對象數組，例如： You have an Array of Objects, such as: ~~~ cats = [ { name: "Bubbles" age: 1 }, { name: "Sparkle" favoriteFood: "tuna" } ] ~~~ 但是你想像放字典一樣訪問它，例如`cat["Bubbles"]`。 But you want to access it as a dictionary by key, like`cats["Bubbles"]`. ## 方法 Solution 你需要把數組轉化成一個對象，使用reduce來實現。 You need to convert your array into an Object. Use reduce for this. ~~~ # key = The key by which to index the dictionary Array::toDict = (key) -> @reduce ((dict, obj) -> dict[ obj[key] ] = obj if obj[key]?; return dict), {} ~~~ 用法： To use this: ~~~ catsDict = cats.toDict('name') catsDict["Bubbles"] # => { age: 1, name: "Bubbles" } ~~~ ## Discussion Alternatively, you can use an Array comprehension: ~~~ Array::toDict = (key) -> dict = {} dict[obj[key]] = obj for obj in this when obj[key]? dict ~~~ 如果你使用Underscore.js，你可以創建一個mixin： If you use Underscore.js, you can create a mixin: ~~~ _.mixin toDict: (arr, key) -> throw new Error('_.toDict takes an Array') unless _.isArray arr _.reduce arr, ((dict, obj) -> dict[ obj[key] ] = obj if obj[key]?; return dict), {} catsDict = _.toDict(cats, 'name') catsDict["Sparkle"] # => { favoriteFood: "tuna", name: "Sparkle" } ~~~