Javascript - 清除数组对象的重复项 [英] Javascript - clearing duplicates from an array object

问题描述

嗨
我有一个javascript数组对象，代表在给定国家/地区销售的商品数量，如下所示：

Hi I have a javascript array object rapresenting the amount of items sold in a given country, like this:

var data = [{'c1':'USA', 'c2':'Item1', 'c3':100}, 
            {'c1':'Canada', 'c2':'Item1', 'c3':120},
            {'c1':'Italy', 'c2':'Item2', 'c3':140},
            {'c1':'Italy', 'c2':'Item2', 'c3':110}]

我需要避免重复（如你可能会看到，最后两个'记录'具有相同的国家和相同的项目）并将金额相加;如果我从数据库获取数据，我将使用DISTINCT SUM子句，但在这种情况下呢？有没有什么好的jquery技巧？

I need to avoid duplicates (as you may see, the last two 'records' have the same Country and the same Item) and sum the amounts; if I was getting data from a database I would use the DISTINCT SUM clause, but what about it in this scenario? Is there any good jquery trick?

推荐答案

你可以使用一个对象作为不同值的映射，如下所示：

You could use an object as a map of distinct values, like this:

var distincts, index, sum, entry, key;
distincts = {};
sum = 0;
for (index = 0; index < data.length; ++index) {
    entry = data[index];
    key = entry.c1 + "--sep--" + entry.c2;
    if (!distincts[key]) {
        distincts[key] = true;
        sum += entry.c3;
    }
}

如何运作： JavaScript对象是映射，并且由于对属性的访问是极常见操作，因此一个不错的JavaScript实现试图使属性访问非常快（通过在属性键上使用散列，这种事情）。您可以使用括号（ [] ）使用字符串作为名称来访问对象属性，所以 obj.foo 和 obj [foo] 都引用 obj foo 属性c $ c>。

How that works: JavaScript objects are maps, and since access to properties is an extremely common operation, a decent JavaScript implementation tries to make property access quite fast (by using hashing on property keys, that sort of thing). You can access object properties using a string for their name, by using brackets ([]), so obj.foo and obj["foo"] both refer to the foo property of obj.

所以：

1. 我们从一个对象开始没有属性。


2. 当我们遍历数组时，我们从 c1 和 c2 <创建唯一键/ code>。重要的是--sep--字符串是不能出现在 c1 或 c2 。如果情况不重要，您可以在那里抛出 .toLowerCase 。


3. 如果区分已经有一个该键的值，我们知道我们之前已经看过它，我们可以忽略它;否则，我们在这种情况下添加一个值（ true ，但它可以是 false 以外的任何其他值， undefined ， 0 ，或）作为标志指示我们之前见过这种独特的组合。我们将 c3 添加到总和中。

1. We start with an object with no properties.
2. As we loop through the array, we create unique key from c1 and c2. It's important that the "--sep--" string be something that cannot appear in c1 or c2. If case isn't significant, you might throw a .toLowerCase in there.
3. If distincts already has a value for that key, we know we've seen it before and we can ignore it; otherwise, we add a value (true in this case, but it can be just about anything other than false, undefined, 0, or "") as a flag indicating we've seen this unique combination before. And we add c3 to the sum.

但有人指出，你的最后两个条目实际上并不相同;我猜这只是问题上的一个错字......

But as someone pointed out, your last two entries aren't actually the same; I'm guessing that was just a typo in the question...

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