Exclude element in array when iterating using map

Question

I have code like below

let myNums = getXYZ(nums: [1,2,3,4,5])

func getXYZ(nums: [Int]) -> [Int] {
let newNum = nums.map { (num) -> Int in

    if num == 2 {
    //do something and continue execution with next element in list like break/fallthrough
        return 0
    }
    return num
}

return newNum

}

print(myNums)`

This prints [1,0,3,4,5]

but i want the output to be [1,3,4,5]. How can I exclude 2? I want to alter the if statement used so as to not include in array when it sees number 2

I have to use .map here but to exclude 2..is there any possibility

Please let me know

flatMap is depraced also it returns same error even with flatMap " nil is incompatible with return type 'Int'". I tried if num == 2 { return nil } — Ashh
– Ashh, Commented Feb 11, 2019 at 2:12
Like what koropok said use compactMap and inside your closure make your return type nullable like so (num) -> Int? — Zonily Jame
– Zonily Jame, Commented Feb 11, 2019 at 2:17

impression7vx · Accepted Answer · 2019-02-11 02:30:12Z

1

I'd simply do a filter as described as your problem, you want to filter the numbers by removing another number.

var myNums = [1, 2, 3, 4, 5]
let excludeNums = [2]

let newNum = myNums.filter({ !excludeNums.contains($0) })

print(newNum) //1, 3, 4, 5

If you need to do a map, you could do a map first then filter.

let newNum = myNums.map({ $0*2 }).filter({ !excludeNums.contains($0) })
print(newNum) //4, 6, 8, 10

This maps to multiplying both by 2 and then filtering by removing the new 2 from the list. If you wanted to remove the initial 2 you would have to filter first then map. Since both return a [Int] you can call the operations in any order, as you deem necessary.

edited Feb 11, 2019 at 2:30

answered Feb 11, 2019 at 2:24

impression7vx

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Comments

Ashh · Accepted Answer · 2019-02-11 02:34:10Z

1

As suggested by @koropok, I had to make below changes

nums.compactMap { (num) -> Int? in .... if num == 2 { return nil }

answered Feb 11, 2019 at 2:34

Ashh

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1 Comment

koropok Over a year ago

you can just use Shorthand Argument Names for inline closures. remove (num) -> int? and replace num == 2 with $0 == 2.

qtngo · Accepted Answer · 2019-02-11 02:36:42Z

1

I suggest you to use filter instead of map:

let myNums = [1,2,3,4,5]
let result1 = myNums.filter{ return $0 != 2 }
print(result1) // This will print [1,3,4,5]

If you must definitely use map, then use compactMap:

let result2 = myNums.compactMap { return $0 == 2 ? nil : $0 }
print(result2) // This will print [1,3,4,5]

Hope this helps

answered Feb 11, 2019 at 2:36

qtngo

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1 Comment

Neph Over a year ago

You can shorten the compactMap version by getting rid of the return (in Swift 5, at least).

Code Different · Accepted Answer · 2019-02-11 04:40:47Z

1

filter is more appropriate than map for your use case.

If you want to exclude only 1 number:

func getXYZ(nums: [Int]) -> [Int] {
    return nums.filter { $0 != 2 }
}

If you want to exclude a list of numbers, store those exclusions in a Set since Set.contains runs in O(1) time, whereas Array.contains runs in O(n) time.

func getXYZ(nums: [Int]) -> [Int] {
    let excluded: Set<Int> = [2,4]
    return nums.filter { !excluded.contains($0) }
}

answered Feb 11, 2019 at 4:40

Code Different

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Comments

bsorrentino · Accepted Answer · 2022-11-02 17:24:50Z

0

My solution is based on enumerated() method:

let elements = nums.enumerated().compactMap { (index, value) in
                    ( index == 0 ) ? nil : value
                }

enumerated() add element's index as first closure argument

answered Nov 2, 2022 at 17:24

bsorrentino

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