您可以使用集合的min方法将其索引与元素压缩,并传递一个谓词来比较元素的最小值。获取结果并提取元组的索引:
let numbers = [2, 4, 4, 2, 3, 1]
let minIndex = zip(numbers.indices, numbers).min(by: { $0.1 < $1.1 })?.0
let maxIndex = zip(numbers.indices, numbers).max(by: { $0.1 < $1.1 })?.0
作为一个元素可比较的扩展:
extension Collection where Element: Comparable {
func firstIndexOfMaxElement() -> Index? {
zip(indices, self).max(by: { $0.1 < $1.1 })?.0
}
func firstIndexOfMinElement() -> Index? {
zip(indices, self).min(by: { $0.1 < $1.1 })?.0
}
}
使用方法:
numbers.firstIndexOfMinElement() // 5
如果您需要找到最大或最小属性:
extension Collection {
func firstIndexOfMaxElement<T: Comparable>(_ predicate: (Element) -> T) -> Index? {
zip(indices, self).max(by: { predicate($0.1) < predicate($1.1) })?.0
}
func firstIndexOfMinElement<T: Comparable>(_ predicate: (Element) -> T) -> Index? {
zip(indices, self).min(by: { predicate($0.1) < predicate($1.1) })?.0
}
}
使用方法:
struct Product {
let price: Int
}
let products: [Product] = [.init(price: 2),
.init(price: 4),
.init(price: 4),
.init(price: 2),
.init(price: 3),
.init(price: 1),]
let minPrice = products.firstIndexOfMinElement(\.price)
返回最大和最小元素及其索引:
extension Collection where Element: Comparable {
func maxElementAndIndices() -> (indices: [Index], element: Element)? {
guard let maxValue = self.max() else { return nil }
return (indices.filter { self[$0] == maxValue }, maxValue)
}
func minElementAndIndices() -> (indices: [Index], element: Element)? {
guard let minValue = self.min() else { return nil }
return (indices.filter { self[$0] == minValue }, minValue)
}
}
对于自定义的结构/类,有相应的方法:
extension Collection {
func maxElementsAndIndices<T: Comparable>(_ predicate: (Element) -> T) -> [(index: Index, element: Element)] {
guard let maxValue = self.max(by:{ predicate($0) < predicate($1)}) else { return [] }
return zip(indices, self).filter { predicate(self[$0.0]) == predicate(maxValue) }
}
func minElementsAndIndices<T: Comparable>(_ predicate: (Element) -> T) -> [(index: Index, element: Element)] {
guard let minValue = self.min(by:{ predicate($0) < predicate($1)}) else { return [] }
return zip(indices, self).filter { predicate(self[$0.0]) == predicate(minValue) }
}
}
使用方法:
let maxNumbers = numbers.maxElementAndIndices() // ([1, 2], element 4)
let minNumbers = numbers.minElementAndIndices() // ([5], element 1)
let maxPriceIndices = products.maxElementsAndIndices(\.price) // [(index: 1, element: Product(price: 4)), (index: 2, element: Product(price: 4))]
let minPriceIndices = products.minElementsAndIndices(\.price) // [(index: 5, element: __lldb_expr_22.Product(price: 1))]