How to remove nil elements from an array in Swift

If you have an array with optional values, you can easily filter out nil elements from that array using the compactMap(_:) method.

In the following example, we have an optional string array, optionalColors. You can filter nil value out of any array by calling compactMap(_:) on that array.

let optionalNumbers: [String?] = ["1", "2", nil, "3", "four"]
let nonOptionalNumbers: [String] = optionalNumbers.compactMap { $0 }
print(nonOptionalNumbers)
// ["1", "2", "3", "four"]

A compact map is a map function but more compact (no nil value). You can make any transform with each element in the passing closure, and compactMap will make sure there is no nil value in the resulting array.

Here is another example where we try to parse a number String into an Int.

let optionalNumbers = ["1", "2", nil, "3", "four"]       
let nonOptionalNumbers = optionalNumbers.compactMap { numberString in
    if let numberString {
        // 1
        return Int(numberString)
    } else {
        return nil
    }
}
print(nonOptionalNumbers)
// [1, 2, 3]

1 Parsing a string into an integer is a failable constructor, init?(_ description: String), but compactMap will ensure the resulting array contains only non-nil values.