iOS版雨燕：滤镜阵列，以独特的项目 [英] iOS Swift: Filter array to unique items

问题描述

我有一个数组，看起来像这样：

I have an array that looks like this:

let records = [
    ["created": NSDate(timeIntervalSince1970: 1422600000), "type": 0],
    ["created": NSDate(timeIntervalSince1970: 1422600000), "type": 0],
    ["created": NSDate(timeIntervalSince1970: 1422600000), "type": 1],
    ["created": NSDate(timeIntervalSince1970: 1422600000), "type": 1],
    ["created": NSDate(timeIntervalSince1970: 1422700000), "type": 2],
    ["created": NSDate(timeIntervalSince1970: 1422700000), "type": 2],
]

我将如何以独特的类型数组只记录过滤？

How would I filter the array to only records with unique types?

推荐答案

尝试：

var seenType:[Int:Bool] = [:]
let result = records.filter {
    seenType.updateValue(false, forKey: $0["type"] as Int) ?? true
}

这基本上code是下面的快捷方式：

Basically this code is a shortcut of the following:

let result = records.filter { element in
    let type = element["type"] as Int

    // .updateValue(false, forKey:) 
    let retValue:Bool? = seenType[type]
    seenType[type] = false

    // ?? true
    if retValue != nil {
        return retValue!
    }
    else {
        return true
    }
}

updateValue 词典返回旧值的如果该键不存在，或者无，如果它是一个新的密钥。

updateValue of Dictionary returns old value if the key exists, or nil if it's a new key.

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