java - 如何分组并删除重复的对象

Question

我有这个 Item 类:

data class Product(val id: Long, val name: String, val region: Long)

给定一个列表List<Product> :

Product(1, "Product 1", 1)
Product(1, "Product 1", 1)
Product(1, "Product 1", 2)
Product(2, "Product 2", 1)

如您所见，同一产品可以多次添加到同一区域。我想按区域分组 productList.groupBy { it.region }但在生成的 map 条目中，我想删除具有相同 ID 的产品。

Answer 1

productList.groupBy { it.region }.mapValues { it.distinctBy { it.id } }

mapValues :

Returns a new map with entries having the keys of this map and the values obtained by applying the transform function to each entry in this Map.

distinctBy :

Returns a list containing only elements from the given collection having distinct keys returned by the given selector function.