# flatten方法 將多維集合轉為一維。 ``` $collection = collect(['name' => 'taylor', 'languages' => ['php', 'javascript']]); $flattened = $collection->flatten(); $flattened->all(); // ['taylor', 'php', 'javascript']; ``` 還可以選擇性地傳入「深度」參數： ``` $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'], ] */ ``` 在這個例子里，調用 flatten 方法時不傳入深度參數的話也會將嵌套數組轉成一維的，然后返回 `['iPhone 6S', 'Apple', 'Galaxy S7', 'Samsung']`，傳入深度參數能限制設置返回數組的層數。