Question

我有一个基于这种结构的json数组：

[
    {property1: "bmw", property2: value, property3: value, property4: value},
    {property1: "mercedes", property2: value, property3: value, property4: value},
    {property1: "bmw", property2: value, property3: value, property4: value},
    {property1: "nissan", property2: value, property3: value, property4: value}
]

我如何过滤数组以查找第一次为property1显示新值并将其存储在单独的数组中？

我希望数组如：["bmw", "mercedes", "nissan"]

Answer 1

如果要存储唯一值，则应使用内置的JavaScript Set()

方法0只会在.add(value)尚未存在的情况下附加value

＆＃13;

let carNames = new Set();
let cars= [
    { property1: "bmw" },
    { property1: "mercedes" },
    { property1: "bmw" },
    { property1: "nissan" }
];

cars.forEach(car => carNames.add(car.property1));

console.log(carNames.size);
for (let name of carNames) {
   console.log(name);
}

＆＃13;

Answer 2

您可以创建一个数组carNames，遍历您的汽车，每次carNames数组中都不包含汽车的property1时，添加它

    var cars= [
    {property1: "bmw", property2: "d", property3: "", property4: "value"},
    {property1: "mercedes", property2: "value", property3: "value", property4: "value"},
    {property1: "bmw", property2: "value", property3: "value", property4: "value"},
    {property1: "nissan", property2: "value", property3: "value", property4: "value"}
];

var carNames = [];
cars.forEach(function(car){
    if (! carNames.includes(car.property1))
        carNames.push(car.property1);
});

Answer 3

鉴于原始数据的结构，我使用属性作为键将数组缩减为Map

＆＃13;

var cars= [
    {property1: "bmw", property2: "d", property3: "", property4: "value"},
    {property1: "mercedes", property2: "value", property3: "value", property4: "value"},
    {property1: "bmw", property2: "value", property3: "value", property4: "value"},
    {property1: "nissan", property2: "value", property3: "value", property4: "value"}
];

var m = cars.reduce((map, entry) => {
	if (!map.has(entry.property1)) {
		map.set(entry.property1, entry)
	}
	return map
}, new Map())

console.log([...m.values()]);
console.log([...m.keys()]);

＆＃13;

然后，您可以使用.values()提取条目以获取完整对象，或.keys()仅获取唯一品牌名称

Array.filter的第一个值

3 个答案: