Laravel Collection 常用方法（1）

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1、first

返回集合第一个通过指定测试的元素：

collect([1, 2, 3, 4])->first();

// 1

collect([1, 2, 3, 4])->first(function ($value, $key) {
    return $value > 2;
});

// 3

2、last

返回集合中，最后一个通过指定测试的元素：

collect([1, 2, 3, 4])->last(function ($value, $key) {
    return $value < 3;
});

// 2

collect([1, 2, 3, 4])->last();

// 4

3、keyBy

以指定键的值作为集合项目的键。如果几个数据项有相同的键，那在新集合中只显示最后一项：

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

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

$keyed->all();

/*
    [
        'prod-100' => ['product_id' => 'prod-100', 'name' => 'Desk'],
        'prod-200' => ['product_id' => 'prod-200', 'name' => 'Chair'],
    ]
*/

$keyed = $collection->keyBy(function ($item) {
    return strtoupper($item['product_id']);
});

$keyed->all();

/*
    [
        'PROD-100' => ['product_id' => 'prod-100', 'name' => 'Desk'],
        'PROD-200' => ['product_id' => 'prod-200', 'name' => 'Chair'],
    ]
*/

4、map

遍历整个集合并将每一个数值传入回调函数。回调函数可以任意修改并返回项目，形成修改过的项目组成的新集合

$collection = collect([1, 2, 3, 4, 5]);

$multiplied = $collection->map(function ($item, $key) {
    return $item * 2;
});

$multiplied->all();

// [2, 4, 6, 8, 10]

5、mapWithKeys

遍历整个集合并将每一个数值传入回调函数。回调函数返回包含一个键值对的关联数组

$collection = collect([
    [
        'name' => 'John',
        'department' => 'Sales',
        'email' => 'john@example.com'
    ],
    [
        'name' => 'Jane',
        'department' => 'Marketing',
        'email' => 'jane@example.com'
    ]
]);

$keyed = $collection->mapWithKeys(function ($item) {
    return [$item['email'] => $item['name']];
});

$keyed->all();

/*
    [
        'john@example.com' => 'John',
        'jane@example.com' => 'Jane',
    ]
*/

6、merge

合并数组进集合。数组「键」对应的数值会覆盖集合「键」对应的数值：

$collection = collect(['product_id' => 1, 'price' => 100]);

$merged = $collection->merge(['price' => 200, 'discount' => false]);

$merged->all();

// ['product_id' => 1, 'price' => 200, 'discount' => false]

7、only

返回集合中指定键的所有项目

$collection = collect(['product_id' => 1, 'name' => 'Desk', 'price' => 100, 'discount' => false]);

$filtered = $collection->only(['product_id', 'name']);

$filtered->all();

// ['product_id' => 1, 'name' => 'Desk']

8、pluck

获取集合中指定「键」所有对应的值

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

$plucked = $collection->pluck('name');

$plucked->all();

// ['Desk', 'Chair']

$plucked = $collection->pluck('name', 'product_id');

$plucked->all();

// ['prod-100' => 'Desk', 'prod-200' => 'Chair']

9、reduce

reduce 方法将集合缩减到单个数值，该方法会将每次迭代的结果传入到下一次迭代

$collection = collect([1, 2, 3]);

$total = $collection->reduce(function ($carry, $item) {
    return $carry + $item;
});

// 6

第一次迭代时 $carry 的数值为 null；然而你也可以传入第二个参数进 reduce 以指定它的初始值：

$collection->reduce(function ($carry, $item) {
    return $carry + $item;
}, 4);

// 10

10、search

search 方法在集合内搜索指定的数值并返回找到的键。假如找不到项目，则返回 false

$collection = collect([2, 4, 6, 8]);

$collection->search(4);

// 1

$collection->search(function ($item, $key) {
    return $item > 5;
});

// 2