# 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。