I have two arrays
var array1 = new Array ["a", "b", "c", "d", "e"]
var array2 = new Array ["a", "c", "d"]
I want to remove elements of array2 from array1
Result ["b", "e"]
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9 Answers
@Antonio's solution is more performant, but this preserves ordering, if that's important:
var array1 = ["a", "b", "c", "d", "e"]
let array2 = ["a", "c", "d"]
array1 = array1.filter { !array2.contains($0) }
7 Comments
RoLYroLLs
loving this method
Tung Fam
good answer! but do you know how to write this on obj-c ? please help me out :) thanks
Robert
If the elements are
Hashable like they are in this case, it might be more performant to convert array2 into a Set first; this would still preserve the order as array1 remains an array, but you can perform fast lookups on the search collection.
C0D3
To make it work, your object also has to conform to the Equatable protocol. If it doesn't you get this weird error in Swift 4.0 saying: Missing argument label 'where:' in call in the contains function inside the filter.
Fede Cugliandolo
@c1pherB1t yes, you can add the
where:in the contains i.e. array1 = array1.filter({ item in !array2.contains(where: { $0.id == item.id }) }) |
The easiest way is to convert both arrays to sets, subtract the second from the first, convert to the result to an array and assign it back to array1:
array1 = Array(Set(array1).subtracting(array2))
Note that your code is not valid Swift - you can use type inference to declare and initialize both arrays as follows:
var array1 = ["a", "b", "c", "d", "e"]
var array2 = ["a", "c", "d"]
6 Comments
Duncan C
Can you subtract an array from a set? Wouldn't that need to be
array1 = Array(Set(array1).subtract(Set(array2))) (Converting Array2 to a set before subtracting it from array1?)
Antonio
@DuncanC: the
subtract method (as well as many other Set methods) takes a SequenceType argument, so yes, you can pass an array.
AmitaiB
I use:
/* Swift 3.x */ func - <Element: Hashable>(lhs: [Element], rhs: [Element]) -> [Element] { return Array(Set<Element>(lhs).subtracting(Set<Element>(rhs))) }
Gordon Childs
That's really nice - it also seems to respect the original order - is that always guaranteed?
Sindre Sorhus
The order is not guaranteed: > An unordered collection of unique elements. developer.apple.com/documentation/swift/set
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Remove elements using indexes array:
Array of Strings and indexes
let animals = ["cats", "dogs", "chimps", "moose", "squarrel", "cow"] let indexAnimals = [0, 3, 4] let arrayRemainingAnimals = animals .enumerated() .filter { !indexAnimals.contains($0.offset) } .map { $0.element } print(arrayRemainingAnimals) //result - ["dogs", "chimps", "cow"]Array of Integers and indexes
var numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] let indexesToRemove = [3, 5, 8, 12] numbers = numbers .enumerated() .filter { !indexesToRemove.contains($0.offset) } .map { $0.element } print(numbers) //result - [0, 1, 2, 4, 6, 7, 9, 10, 11]
Remove elements using element value of another array
Arrays of integers
let arrayResult = numbers.filter { element in return !indexesToRemove.contains(element) } print(arrayResult) //result - [0, 1, 2, 4, 6, 7, 9, 10, 11]Arrays of strings
let arrayLetters = ["a", "b", "c", "d", "e", "f", "g", "h", "i"] let arrayRemoveLetters = ["a", "e", "g", "h"] let arrayRemainingLetters = arrayLetters.filter { !arrayRemoveLetters.contains($0) } print(arrayRemainingLetters) //result - ["b", "c", "d", "f", "i"]
Comments
You can create sets and then use the subtract method
let setA = Set(arr1)
let setB = Set(arr2)
setA.subtract(setB)
2 Comments
Dev Imak
intersect show the elements in common , i want to delete the elements in common and get the others in another array
Adnan Aftab
I update the code, for that you need to use subtract
Here is an extension with @jrc answer:
extension Array where Element: Equatable {
func subtracting(_ array: Array<Element>) -> Array<Element> {
self.filter { !array.contains($0) }
}
}
1 Comment
Alejandro L.Rocha
Nice approach but if you have a million entries this is n^2
out of scope but it would help me if it had been here. removing subArray from array in OBJECTIVE-C
NSPredicate* predicate = [NSPredicate predicateWithFormat:@"not (self IN %@)", subArrayToBeDeleted];
NSArray* finalArray = [initialArray filteredArrayUsingPredicate:predicate];
hope it will ever help someone :)
1 Comment
jrc
That’s not very efficient. Just do this:
[[array1 mutableCopy] removeObjectsInArray:array2]An extended version of the answer by Shai Balassiano:
extension Array where Element: Equatable {
func subtracting(_ array: [Element]) -> [Element] {
self.filter { !array.contains($0) }
}
mutating func remove(_ array: [Element]) {
self = self.subtracting(array)
}
}
Comments
Here is one more solution by defining your own PredicateSet.
struct PredicateSet<A> {
let contains: (A) -> Bool
}
let animals = ["Cow", "Bulldog", "Labrador"]
let dogs = ["Bulldog", "Labrador"]
let notDogs = PredicateSet { !dogs.contains($0) }
print(animals.filter(notDogs.contains)) // ["Cow"]
Comments
If there are 2 arrays which contains duplicated element, and you need just a simple subtraction, You can use this code. This works for String type as well.
extension Array where Element: Equatable {
func subtracting(_ array: Array<Element>) -> Array<Element> {
var result: Array<Element> = []
var toSub = array
for i in self {
if let index = toSub.firstIndex(of: i) {
toSub.remove(at: index)
continue
}
else {
result.append(i)
}
}
return result
}
}
let first = [1, 1, 2, 3, 3, 5, 6, 7, 7]
let second = [2, 2, 3, 4, 4, 5, 5, 6]
let result = first.subtracting(second)
//print result
//[1, 1, 3, 7, 7]
