Removing objects from an array based on another array

Question

I have two arrays like this:

var arrayA = [\"Mike\", \"James\", \"Stacey\", \"Steve\"]
var arrayB = [\"Steve\", \"Gemma\", \"James\", \"Lucy\"]

Answer 1

Using the Array → Set → Array method mentioned by Antonio, and with the convenience of an operator, as freytag pointed out, I've been very satisfied using this:

// Swift 3.x/4.x
func - <Element: Hashable>(lhs: [Element], rhs: [Element]) -> [Element]
{
    return Array(Set<Element>(lhs).subtracting(Set<Element>(rhs)))
}

Answer 2

For smaller arrays I use:

/* poormans sub for Arrays */

extension Array where Element: Equatable {

    static func -=(lhs: inout Array, rhs: Array) {

        rhs.forEach {
            if let indexOfhit = lhs.firstIndex(of: $0) {
                lhs.remove(at: indexOfhit)
            }
        }
    }

    static func -(lhs: Array, rhs: Array) -> Array {

        return lhs.filter { return !rhs.contains($0) }
    }
}

Answer 3

@francesco-vadicamo's answer in Swift 2/3/4+

 arrayA = arrayA.filter { !arrayB.contains($0) }

Answer 4

Original answer

This can also be implemented as a minus func:

func -<T:RangeReplaceableCollectionType where T.Generator.Element:Equatable>( lhs:T, rhs:T ) -> T {

    var lhs = lhs
    for element in rhs {
        if let index = lhs.indexOf(element) { lhs.removeAtIndex(index) }
    }

    return lhs
}

Now you can use

arrayA - arrayB

---

Updated implementation for Swift 5

func -<T: RangeReplaceableCollection>(lhs: T, rhs: T) -> T where T.Iterator.Element: Equatable {

    var lhs = lhs
    for element in rhs {
        if let index = lhs.firstIndex(of: element) { lhs.remove(at: index) }
    }

    return lhs
}

Answer 5

I agree with Antonio's answer, however for small array subtractions you can also use a filter closure like this:

let res = arrayA.filter { !contains(arrayB, $0) }

Answer 6

matt and freytag's solutions are the ONLY ones that account for duplicates and should be receiving more +1s than the other answers.

Here is an updated version of matt's answer for Swift 3.0:

var arrayA = ["Mike", "James", "Stacey", "Steve"]
var arrayB = ["Steve", "Gemma", "James", "Lucy"]
for word in arrayB {
    if let ix = arrayA.index(of: word) {
        arrayA.remove(at: ix)
    }
}