javascript - 合并对象数组中的重复对象

Question

我有以下对象数组，

var data = [
    {
        label: "Book1",
        data: "US edition"
    },
    {
        label: "Book1",
        data: "UK edition"
    },
    {
        label: "Book2",
        data: "CAN edition"
    }
];

我想根据属性“标签”合并重复的对象这样最终输出将如下所示，

var data = [
    {
        label: "Book1",
        data: ["US edition", "UK edition"] //data attribute is merged
    },
    {
        label: "Book2",
        data: "CAN edition"
    }
];

有人可以帮我确定方法吗？

Answer 1

我可能会使用 filter 进行循环，跟踪我之前见过的对象 map ，沿着这些线(编辑以反射(reflect)您同意是的，它是有意义的使 (entry).data 总是一个数组):

var seen = {};
data = data.filter(function(entry) {
    var previous;

    // Have we seen this label before?
    if (seen.hasOwnProperty(entry.label)) {
        // Yes, grab it and add this data to it
        previous = seen[entry.label];
        previous.data.push(entry.data);

        // Don't keep this entry, we've merged it into the previous one
        return false;
    }

    // entry.data probably isn't an array; make it one for consistency
    if (!Array.isArray(entry.data)) {
        entry.data = [entry.data];
    }

    // Remember that we've seen it
    seen[entry.label] = entry;

    // Keep this one, we'll merge any others that match into it
    return true;
});

在 ES6 环境中，我会使用 seen = new Map() 而不是 seen = {}。

注意:Array.isArray 是由 ES5 定义的，因此一些较旧的浏览器(如 IE8)不会包含它。不过，它可以很容易地填充/填充:

if (!Array.isArray) {
    Array.isArray = (function() {
        var toString = Object.prototype.toString;
        return function(a) {
            return toString.call(a) === "[object Array]";
        };
    })();
}

旁注:我可能还会总是将 entry.data 设为一个数组，即使我没有看到它的两个值，因为一致数据结构更容易处理。我没有在上面那样做，因为当只有一个匹配的条目时，你的最终结果显示 data 只是一个字符串。 (我们现在已经在上面做了。)

实例(ES5 版本):

var data = [
    {
        label: "Book1",
        data: "US edition"
    },
    {
        label: "Book1",
        data: "UK edition"
    },
    {
        label: "Book2",
        data: "CAN edition"
    }
];
snippet.log("Before:");
snippet.log(JSON.stringify(data, null, 2), "pre");
var seen = {};
data = data.filter(function(entry) {
    var previous;

    // Have we seen this label before?
    if (seen.hasOwnProperty(entry.label)) {
        // Yes, grab it and add this data to it
        previous = seen[entry.label];
        previous.data.push(entry.data);

        // Don't keep this entry, we've merged it into the previous one
        return false;
    }

    // entry.data probably isn't an array; make it one for consistency
    if (!Array.isArray(entry.data)) {
        entry.data = [entry.data];
    }

    // Remember that we've seen it
    seen[entry.label] = entry;

    // Keep this one, we'll merge any others that match into it
    return true;
});
snippet.log("After:");
snippet.log(JSON.stringify(data, null, 2), "pre");

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