在地图上获取下一个值？

Question

我正在尝试将元素与集合中的下一个元素进行比较.

例如 :

let array: [(Double, String)]= [(2.3, "ok"),
                                (1.4, "ok"),
                                (5.1, "notOk")]

我需要一个返回的数组,它将汇总字符串相同的元素.所以我的结果将是:

new array = [(3.7, "ok"), (5.1, "notOk")]

如果可能的话,我需要做它的功能.我试图在地图中获取下一个元素,但无法找到.

像这样的东西(这只是为了逻辑,这段代码不起作用.

let newArray = array.map {(element, nextElement) in 
    if element.1 == nextElement.1 {
        return element.0 + nextElement.0 
    }
} 

Answer 1

以更实用的方式:

let array: [(Double, String)]= [(2.3, "ok"),
                                (1.4, "ok"),
                                (5.1, "notOk")]
let keys = Set(array.map{$0.1})            // find unique keys
let result = keys.map { key -> (Double, String) in   
    let sum = array.filter {$0.1 == key}   // find all entries with the current key
                   .map {$0.0}             // map them to their values
                   .reduce(0, +)           // sum the values
    return (sum, key)
}
print(result)

输出:

[(5.0999999999999996,"notOk"),(3.6999999999999997,"ok")]

或者(由@dfri建议):

let keys = Set(array.map{$0.1})            // find unique keys
let result = keys.map { key -> (Double, String) in   
    let sum = array.reduce(0) { $0 + ($1.1 == key ? $1.0 : 0) }
    return (sum, key)
}