Swift通用数组函数查找元素的所有索引都不匹配项目 [英] Swift generic array function to find all indexes of elements not matching item
问题描述
示例
let arr:[String] = [Empty,Empty,Full空,全]
让结果:[Int] = arr.indexes(ofItemsNotEqualTo item:Empty)
//返回[2,4]
$ c $
<$ c $
我尝试了一个通用函数: c>扩展数组{
func索引< T:可比较>(ofItemsNotEqualTo item:T) - > [INT]? {
var result:[Int] = []
for self.enumerated(){
if elem!= item {
result.append(n )
}
}
返回result.isEmpty? nil:result
}
}
但是这给出了一个警告:二元运算符不能应用于元素和T类型的操作数。
所以我做了这个我投的元素(注意 扩展数组{
func索引< T:可等分>(ofItemsNotEqualTo item:T) - > [INT]? {
var result:[Int] = [] $ b $ for(n,elem)in self.enumerated(){
if elem as? T!= item {
result.append(n)
}
}
return result.isEmpty? nil:result
}
}
但是现在看起来类型检查有出去了窗口,因为如果我传入一个整数,我得到了错误的结果
let arr:[String] = [
让结果:[Int] = arr.indexes(ofItemsNotEqualTo item:100)
//返回[0,1 ,2,3,4]
帮助将不胜感激。
使用 reduce 函数有更好的方法吗?
您已经定义了一个泛型方法
func索引< T:Equatable>(ofItemsNotEqualTo item :T)→> [INT]?
它的参数类型为 T
which必须是
Equatable
,但与数组的 Element
类型无关。
因此
let arr = [Empty,Empty,完整,空白,全部]
let result = arr.indexes(ofItemsNotEqualTo:100)
编译,但 nil
(这是!= item
)
元素。
你想要的是一种仅为
Equatable
元素数组定义的方法。这可以通过限制的
扩展来实现:
扩展数组其中元素:Equatable {
func索引(ofItemsNotEqualTo item:Element) - > [INT]? {
var result:[Int] = [] $ b $ for(n,elem)in enumerated(){
if elem!= item {
result.append(n)
}
}
返回result.isEmpty? nil:result
}
}
其实我不会让返回值可选。
如果所有元素都等于给定项目,那么逻辑
返回值就是空数组。 >有没有更好的方法来使用reduce函数做到这一点?
好的,你可以 使用 reduce()
,但这不是非常有效,因为在每个迭代步骤中都会创建中间数组:
扩展数组其中元素:Equatable {
func索引(ofItemsNotEqualTo item:Element) - > [Int] {
return enumerated()。reduce([]){
$ 1.element == item? $ 0:$ 0 + [$ 1.offset]
}
}
}
你实际上有一个
filter + map操作:
扩展数组其中Element:Equatable {
func索引(ofItemsNotEqualTo item:Element) - > [Int] {
return enumerated()。filter {$ 0.element!= item} .map {$ 0.offset}
}
}
可以使用 flatMap()
简化:
扩展数组其中,Element:Equatable {
func索引(ofItemsNotEqualTo item:Element) - > [Int] {
return enumerated()。flatMap {$ 0.element!= item? $ 0.offset:nil}
}
}
示例:
let arr = [Empty,Empty,Full,Empty,Full]
arr .indexes(ofItemsNotEqualTo:Full)// [0,1,3]
[1,1,1] .indexes(ofItemsNotEqualTo:1)// []
arr.indexes(ofItemsNotEqualTo:100)
//错误:无法将'Int'类型的值转换为期望的参数类型'String'
Swift 3
Trying to write a generic array extension that gets all indexes of items that DON'T equal value
example
let arr: [String] = ["Empty", "Empty", "Full", "Empty", "Full"]
let result: [Int] = arr.indexes(ofItemsNotEqualTo item: "Empty")
//returns [2, 4]
I tried to make a generic function:
extension Array {
func indexes<T: Equatable>(ofItemsNotEqualTo item: T) -> [Int]? {
var result: [Int] = []
for (n, elem) in self.enumerated() {
if elem != item {
result.append(n)
}
}
return result.isEmpty ? nil : result
}
}
But that gives a warning: Binary operator cannot be applied to operands of type "Element" and "T".
So then I did this where I cast the element (note the as?)
extension Array {
func indexes<T: Equatable>(ofItemsNotEqualTo item: T) -> [Int]? {
var result: [Int] = []
for (n, elem) in self.enumerated() {
if elem as? T != item {
result.append(n)
}
}
return result.isEmpty ? nil : result
}
}
But now it seems the type checking has gone out the window, because if I pass in an integer I get the wrong result
let arr: [String] = ["Empty", "Empty", "Full", "Empty", "Full"]
let result: [Int] = arr.indexes(ofItemsNotEqualTo item: 100)
//returns [0, 1, 2, 3, 4]
Help would be greatly appreciated.
Is there a better way to do this with the reduce function?
You have defined a generic method
func indexes<T: Equatable>(ofItemsNotEqualTo item: T) -> [Int]?
which takes an argument of type T
which is required to be
Equatable
, but is unrelated to the Element
type of the array.
Therefore
let arr = ["Empty", "Empty", "Full", "Empty", "Full"]
let result = arr.indexes(ofItemsNotEqualTo: 100)
compiles, but elem as? T
gives nil
(which is != item
)
for all array elements.
What you want is a method which is defined only for arrays of
Equatable
elements. This can be achieved with a constrained
extension:
extension Array where Element: Equatable {
func indexes(ofItemsNotEqualTo item: Element) -> [Int]? {
var result: [Int] = []
for (n, elem) in enumerated() {
if elem != item {
result.append(n)
}
}
return result.isEmpty ? nil : result
}
}
Actually I would not make the return value an optional. If all elements are equal to the given item, then the logical return value would be the empty array.
Is there a better way to do this with the reduce function?
Well, you could use reduce()
, but that is not very efficient because intermediate arrays are created in each iteration step:
extension Array where Element: Equatable {
func indexes(ofItemsNotEqualTo item: Element) -> [Int] {
return enumerated().reduce([]) {
$1.element == item ? $0 : $0 + [$1.offset]
}
}
}
What you actually have is a "filter + map" operation:
extension Array where Element: Equatable {
func indexes(ofItemsNotEqualTo item: Element) -> [Int] {
return enumerated().filter { $0.element != item }.map { $0.offset }
}
}
which can be simplified using flatMap()
:
extension Array where Element: Equatable {
func indexes(ofItemsNotEqualTo item: Element) -> [Int] {
return enumerated().flatMap { $0.element != item ? $0.offset : nil }
}
}
Examples:
let arr = ["Empty", "Empty", "Full", "Empty", "Full"]
arr.indexes(ofItemsNotEqualTo: "Full") // [0, 1, 3]
[1, 1, 1].indexes(ofItemsNotEqualTo: 1) // []
arr.indexes(ofItemsNotEqualTo: 100)
// error: cannot convert value of type 'Int' to expected argument type 'String'
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