arrays - 用对象过滤嵌套数组

Question

我有一组类别。每个 Category 实例都有 offers 属性。

class Category {
   var offers : [Offer]?
   var title : String?
   var id : Int?
}

class Offer {
    var type : String?
}

//global variable
var categories = [ categ1, categ2, ...]

如何按 offer.type 筛选类别？

我已经试过了:

return categories.map { (category) -> Category in
    let offers = category.offers?.filter { $0.type == myType }
    category.offers = offers
    return category
}

它有效，但在第二次调用函数后数组变为空。可能是因为报价被重写了？

然后我尝试了这个(产生了同样的错误结果):

var resultCategories = [Category]()

for category in categories {
    guard let offers = category.offers else { continue }

    var newOffers = [Offer]()

    for offer in offers {
        if offer.type == myType {
            newOffers.append(offer)
        }
    }

    category.offers = newOffers
    resultCategories.append(category)
}

return resultCategories

Answer 1

您应该简单地过滤所有没有符合您的类型的商品的类别。您可以通过以下方式实现:

1. 筛选所有类别并
2. 在 filter 中检查当前商品是否包含 myType

代码:

let filtered = categories.filter { category in
    category.offers?.contains(where: { $0.type == myType }) ?? false
}

请注意，category.offers?.[...] 是可选值，所以 ?? false 如果左侧部分为 nil，则返回 false 作为结果。

---

更新。

But I expected that categories will have only offers with type = "A". Maybe I did not described the question accurately.

您可以通过创建一个新的 Category 来实现。

let filtered = categories.compactMap { category -> Category? in
    guard let offers = category.offers?.filter({ $0.type == "A" }) else { return nil }
    let other = Category()
    other.offers = offers
    return other
}

另请注意，我正在使用 compactMap。它允许我过滤出空的或 nil offers 的类别。