iOS Swift: Filter array to unique items

Question

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],
]

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

Which version of Swift you are using? – CRDave Mar 10 '15 at 07:53 — CRDave, Mar 10 '15 at 07:53

rintaro · Answer 1 · 2015-03-10T08:34:31.143

7

Try:

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

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

edited Mar 10 '15 at 08:34

answered Mar 10 '15 at 08:05

rintaro

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You need to explain the answer. Why does this code work etc... – Fogmeister Mar 10 '15 at 08:13
nice one. Good answer. – Fogmeister Mar 10 '15 at 08:37
Elegant! (Even if setting `seenType[type]` to `false` if the type *has* been seen is quite counter-intuitive :) – With Swift 1.2 one could probably use a `Set` for `seenType`. – Martin R Mar 10 '15 at 08:52

score 1 · Answer 2 · answered Mar 10 '15 at 08:16

1

There has got to be a more swift way to do this but it works.

var unique = [Int: AnyObject]()

for record in records {
    if let type = record["type"] as? Int {
        unique[type] = record
    }
}

enter image description here

answered Mar 10 '15 at 08:16

Price Ringo

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iOS Swift: Filter array to unique items

2 Answers2

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