在 Swift 中按值对字典进行排序 [英] Sort Dictionary by values in Swift

问题描述

swift 中是否有类似 - (NSArray *)keysSortedByValueUsingSelector:(SEL)comparator?

Is there are analog of - (NSArray *)keysSortedByValueUsingSelector:(SEL)comparator in swift?

如何在不强制转换为 NSDictionary 的情况下执行此操作?

How to do this without casting to NSDictionary?

我试过了，但似乎不是一个好的解决方案.

I tried this, but it seems to be not a good solution.

var values = Array(dict.values)
values.sort({
    $0 > $1
    })

for number in values {
    for (key, value) in dict {
        if value == number {
            println(key + " : \(value)");
            dict.removeValueForKey(key);
            break
        }
    }
}

示例:

var dict = ["cola" : 10, "fanta" : 12, "sprite" : 8]
dict.sortedKeysByValues(>) // fanta (12), cola(10), sprite(8)

推荐答案

尝试:

let dict = ["a":1, "c":3, "b":2]

extension Dictionary {
    func sortedKeys(isOrderedBefore:(Key,Key) -> Bool) -> [Key] {
        return Array(self.keys).sort(isOrderedBefore)
    }

    // Slower because of a lot of lookups, but probably takes less memory (this is equivalent to Pascals answer in an generic extension)
    func sortedKeysByValue(isOrderedBefore:(Value, Value) -> Bool) -> [Key] {
        return sortedKeys {
            isOrderedBefore(self[$0]!, self[$1]!)
        }
    }

    // Faster because of no lookups, may take more memory because of duplicating contents
    func keysSortedByValue(isOrderedBefore:(Value, Value) -> Bool) -> [Key] {
        return Array(self)
            .sort() {
                let (_, lv) = $0
                let (_, rv) = $1
                return isOrderedBefore(lv, rv)
            }
            .map {
                let (k, _) = $0
                return k
            }
    }
}

dict.keysSortedByValue(<)
dict.keysSortedByValue(>)

更新:

从 beta 3 更新到新的数组语法和排序语义.请注意，我使用 sort 而不是 sorted 来最小化数组复制.通过查看早期版本并将 sort 替换为 sorted 并将 KeyType[] 固定为 ，可以使代码更加紧凑>[KeyType]

Updated to the new array syntax and sort semantics from beta 3. Note that I'm using sort and not sorted to minimize array copying. The code could be made more compact, by looking at the earlier version and replacing sort with sorted and fixing the KeyType[] to be [KeyType]

更新到 Swift 2.2:

Updated to Swift 2.2:

将类型从 KeyType 更改为 Key 并将 ValueType 更改为 Value.使用新的 sort 内置于 Array 而不是 sort(Array) 注意所有这些的性能可以通过使用 sortInPlace 而不是 sort

Changed types from KeyType to Key and ValueType to Value. Used new sort builtin to Array instead of sort(Array) Note performance of all of these could be slightly improved by using sortInPlace instead of sort

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