如何访问Laravel集合中的第n个项目? [英] How to access the nth item in a Laravel collection?

问题描述

我想我是通过故意重复一个问题来打破所有规则的...

I guess I am breaking all the rules by deliberately making a duplicate question...

其他问题有一个可接受的答案.它显然解决了提问者问题，但没有回答标题问题.

The other question has an accepted answer. It obviously solved the askers problem, but it did not answer the title question.

让我们从头开始-first()方法的实现大致如下:

Let's start from the beginning - the first() method is implemented approximately like this:

foreach ($collection as $item)
    return $item;

它显然比采用$collection[0]或使用其他建议的方法更强大.

It is obviously more robust than taking $collection[0] or using other suggested methods.

即使集合中有20个项目，也可能没有索引为0或索引为15的项目.为了说明问题，让我们从文档中取出这个集合:

There might be no item with index 0 or index 15 even if there are 20 items in the collection. To illustrate the problem, let's take this collection out of the docs:

$collection = collect([
    ['product_id' => 'prod-100', 'name' => 'desk'],
    ['product_id' => 'prod-200', 'name' => 'chair'],
]);

$keyed = $collection->keyBy('product_id');

现在，我们是否有任何可靠的(最好是简洁的)方法来访问$keyed的第n个项目?

Now, do we have any reliable (and preferably concise) way to access nth item of $keyed?

我个人的建议是:

$nth = $keyed->take($n)->last();

但是，每当$n > $keyed->count()时，这将给出错误的项目($keyed->last()). 如果第n个项存在，而又不像first()那样，我们怎么得到null?

But this will give the wrong item ($keyed->last()) whenever $n > $keyed->count(). How can we get the nth item if it exists and null if it doesn't just like first() behaves?

为澄清起见，让我们考虑以下集合:

To clarify, let's consider this collection:

$col = collect([
    2 => 'a',
    5 => 'b',
    6 => 'c',
    7 => 'd']);

第一个项目是$col->first().如何获得第二个?

First item is $col->first(). How to get the second?

$col->nth(3)应该返回'c'(如果从0开始，则返回'c'，但这与first()不一致). $col[3]不起作用，它只会返回一个错误.

$col->nth(3) should return 'c' (or 'c' if 0-based, but that would be inconsistent with first()). $col[3] wouldn't work, it would just return an error.

$col->nth(7)应该返回null，因为没有第七项，只有四个. $col[7]不起作用，它只会返回'd'.

$col->nth(7) should return null because there is no seventh item, there are only four of them. $col[7] wouldn't work, it would just return 'd'.

您可以将问题改写为如何以foreach顺序获得第n个项目?"如果对某些人更清楚.

You could rephrase the question as "How to get nth item in the foreach order?" if it's more clear for some.

推荐答案

我想更快，更节省内存的方法是使用 slice() 方法:

I guess faster and more memory-efficient way is to use slice() method:

$collection->slice($n, 1);

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