iOS Swift: Filter array to unique items [duplicate]

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
– CRDave

2015-03-10 07:53:33 +00:00
Commented Mar 10, 2015 at 7:53 — CRDave
– CRDave, Commented Mar 10, 2015 at 7:53

rintaro · Accepted Answer · 2015-03-10 08:34:31Z

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, 2015 at 8:34

answered Mar 10, 2015 at 8:05

rintaro

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3 Comments

Fogmeister Over a year ago

You need to explain the answer. Why does this code work etc...

Fogmeister Over a year ago

nice one. Good answer.

Martin R Over a year ago

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.

Price Ringo · Accepted Answer · 2015-03-10 08:16:23Z

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, 2015 at 8:16

Price Ringo

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