按日期对数组进行排序会产生意想不到的结果 [英] Sort array by date gives unexpected results

问题描述

这听起来是一个简单的问题，但我花了我的星期天试图找出下面描述的我的实现有什么问题，所以我将它发布到 SO 作为最后的手段.

This will sound as an easy problem but I spent my Sunday trying to figure out what's wrong with my implementation described below so I am posting it to SO as a last resort.

我有一个从服务器接收数据结构的 javascript 应用程序.服务器端出于性能原因发送未排序的数据.

I have a javascript application that receives data structures from a server. The server side sends the data unsorted for performance reasons.

这是接收数据的javascript代码片段:

Here is a snippet of the the javascript code receiving data:

    var seriesRawDataArray = ko.observableArray();
    ...
    analyticscontext.series(seriesRawDataArray).done(function () {
        renderSeries();
    });

analyticscontext 模块使用 ajax 查询数据:

The analyticscontext module queries the data using ajax:

function series(seriesData) {
    return $.ajax({
        url: "/api/analytics/series",
        type: "GET",
        success: function (data) {
            return seriesData(data);
        }
    });
}

renderSeries 在渲染数据之前对数据进行排序:

The renderSeries performs a sort on the data before rendering it:

    // Sort the data by date using moment.js
    seriesRawDataArray.sort(function (left, right) {
        var leftDate = moment.utc(left.timeStamp);
        var rightDate = moment.utc(right.timeStamp);
        var diff = leftDate.diff(rightDate);
        return diff > 0;
    });

问题

这是我从我的服务器收到的数据样本:

Here is a data sample I receive from my server:

注意最后未排序的项目.seriesRawDataArray.sort 似乎对原始数组没有影响，无论我如何更改排序方法，原始数组都不会被排序.输出总是:

Notice the unsorted items at the end. the seriesRawDataArray.sort seem to have no effect on the original array which does not get sorted no matter what I change in the sorting method. The output is always:

注意这里未排序的元素.我正在使用的库和数据绝对不是问题，因为这个 jsfiddle 工作得很好！这段代码有问题吗?

Notice the unsorted elements here. The libraries I am using and the data is definitely not the problem as this jsfiddle works just fine! Is there something wrong with this code?

推荐答案

简答

您应该返回两个日期之间的差异，而不是布尔值:

short answer

You should return the difference between the two dates, not a boolean:

// sort the data by date using moment.js
seriesRawDataArray.sort(function (left, right) {
    return moment.utc(left.timeStamp).diff(moment.utc(right.timeStamp))
});

为什么

Array.prototype.sort 期望返回负值、零值或正值.一般来说，你会写一个这样的排序函数:

why

Array.prototype.sort expects a negative, zero, or positive value to be returned. Generally, you'll write a sort function like this:

yourArray.sort(function (a, b) {
    if (a < b) {            // a comes first
        return -1
    } else if (b < a) {     // b comes first
        return 1
    } else {                // equal, so order is irrelevant
        return 0            // note: sort is not necessarily stable in JS
    }
})

^{传递给 sort 的匿名函数用作 sort 函数本机实现的比较器.}

但是，负值不一定是 -1，正值不一定是 +1.因此，在对数字进行排序时，您可以改为使用快捷方式:

However, your negative value doesn't have to be -1 and your positive value doesn't have to be +1. Therefore, when sorting numbers, you can instead use the shortcut:

yourArray.sort(function (a, b) {
    return a - b
})

在 JavaScript 中，减去两个日期会将它们强制转换为数字，这就是为什么我们可以使用 return moment.utc(left.timeStamp).diff(moment.utc(right.timeStamp))

In JavaScript, subtracting two dates coerces them both into numbers, which is why we could use return moment.utc(left.timeStamp).diff(moment.utc(right.timeStamp))

^{(代替直接减法-，该方法使用moment.prototype.diff 来自 moment.js 库)}

^{(instead of direct subtraction -, this method uses moment.prototype.diff from the moment.js library)}

但是，在您的代码中，您返回了 diff >0，可以是 true 或 false.由于类型强制，JavScript 会将 true 读取为 1，将 false 读取为 0.这意味着您的排序函数永远不会返回 -1.因此，您的元素将无法正确排序.

However, in your code, you returned diff > 0, which can be either true or false. Because of type coercion, JavScript will read true as 1 and false as 0. This means your sort function will never return -1. Therefore, your elements will not be sorted correctly.

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