[英]What is the fastest way to categorize arrays using underscore.js?
對於這樣的json對象,
list=[
{name:"hello",
category:"verb"},
{name:"world",
category:"noun"}
];
什么是使用下划線對數組進行分類的最快方法:
category=[
{id:"verb",
list:[
{name:"hello",
category:"verb"}
]},
{id:"noun",
list:[
{name:"world",
category:"noun"}
]}
];
它應該是某種鏈式map-reduce ...當然,我可以使用_.filter
輕松做到這_.filter
(但這會很慢),也可以使用for
循環。
好的,我找到了:
groupBy _.groupBy(列表,迭代器)
將集合分為若干集合,並按通過iterator運行每個值的結果進行分組。 如果iterator是字符串而不是函數,請在每個值上按iterator命名的屬性進行分組。
_.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
=> {1: [1.3], 2: [2.1, 2.4]}
_.groupBy(['one', 'two', 'three'], 'length');
=> {3: ["one", "two"], 5: ["three"]}
所以我用這個(我已經有一個清單)做到了:
var listofwords=_.groupBy(doc.words, function(word){
return word.category;
});
_.each(doc.lists,function(list){
list.words=listofwords[list.name];
});
我認為這應該更快
list = [
{name:"hello", category:"verb"},
{name:"world", category:"noun"}
];
var addresses = {};
var catList = _.reduce(list, function(cat, item) {
var address = addresses[item.category];
if(typeof address == 'undefined') {
addresses[item.category] = address = cat.length;
cat.push({id: item.category, list: []});
}
cat[address].list.push(item);
return cat;
}, []);
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