Swift Warning - Cast from '[(key: String, value: Int)]' to unrelated type '[String : Int]' always fails

Question

Given the dictionary:

let dictionary = [ "one": 1, "two": 2, "three": 3]

I want to create a new version with one of the items removed based on its key. So I'm trying to use...

let dictionaryWithTwoRemoved = dictionary.filter { $0.0 != "two" }

... which achieves what I want HOWEVER the two dictionaries have differing types...

`dictionary` is a `[String: Int]`
`dictionaryWithTwoRemoved` is a `[(key: String, value: Int)]`

Which is consequently making my life difficult.

If I try to cast like so...

let dictionaryWithThreeRemoved = dictionary.filter { $0.0 != "three" } as! [String: Int]

...I get the following WARNING...

Cast from '[(key: String, value: Int)]' to unrelated type '[String : Int]' always fails

and the code also crashes with EXC_BAD_INSTRUCTION at runtime.

Help!

Dictionary does not have a filter function (yet). You are using the filter from Sequence but Dictionary is a sequence of key-value pairs. After calling filter, it's not a dictionary any more, it's a list of key-value pairs. — Sulthan
– Sulthan, Commented Apr 5, 2017 at 19:45
Compare stackoverflow.com/questions/32604897/swift-filter-dictionary. — Martin R
– Martin R, Commented Apr 5, 2017 at 19:46

Victor Gabana · Accepted Answer · 2017-04-10 14:15:06Z

1

If you want an extension method to help you remove the values here you go...

extension Dictionary {
    func removingValue(forKey key: Key) -> [Key: Value] {
        var mutableDictionary = self
        mutableDictionary.removeValue(forKey: key)
        return mutableDictionary
    }
}

answered Apr 10, 2017 at 14:15

Victor Gabana

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user498982 · Accepted Answer · 2017-04-05 20:09:43Z

1

You can use reduce to do this.

//: Playground - noun: a place where people can play

import Cocoa

let dictionary = [ "one": 1, "two": 2, "three": 3]
let newDictionary = dictionary.reduce([:]) { result, element -> [String: Int] in
    guard element.key != "two" else {
        return result
    }

    var newResult = result
    newResult[element.key] = element.value
    return newResult
}

answered Apr 5, 2017 at 20:09

user498982

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