flatten方法

将多维集合转为一维。

$collection = collect(['name' => 'taylor', 'languages' => ['php', 'javascript']]);

$flattened = $collection->flatten();

$flattened->all(); // ['taylor', 'php', 'javascript'];

还可以选择性地传入「深度」参数：

$collection = collect([
    'Apple' => [
        ['name' => 'iPhone 6S', 'brand' => 'Apple'],
    ],
    'Samsung' => [
        ['name' => 'Galaxy S7', 'brand' => 'Samsung']
    ],
]);

$products = $collection->flatten(1);

$products->values()->all();

/*
[
    ['name' => 'iPhone 6S', 'brand' => 'Apple'],
    ['name' => 'Galaxy S7', 'brand' => 'Samsung'],
]
*/

在这个例子里，调用 flatten 方法时不传入深度参数的话也会将嵌套数组转成一维的，然后返回 ['iPhone 6S', 'Apple', 'Galaxy S7', 'Samsung']，传入深度参数能限制设置返回数组的层数。