iOS Swift:将数组过滤为唯一项目

Question

我有一个看起来像这样的数组:

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],
]

如何将数组过滤为仅包含唯一类型的记录？

Answer 1

尝试:

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

基本上这段代码是以下的快捷方式:

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的Dictionary返回旧值,如果键不存在,或者nil如果它是一个新的密钥.