Skip item when performing map in Swift?

Question

I\'m applying a map to a dictionary that has a try in it. I\'d like to skip the iteration if the mapped item is invalid.

For example:

fu         


        

Answer 1

Just replace map() by flatMap():

extension SequenceType {
    /// Returns an `Array` containing the non-nil results of mapping
    /// `transform` over `self`.
    ///
    /// - Complexity: O(*M* + *N*), where *M* is the length of `self`
    ///   and *N* is the length of the result.
    @warn_unused_result
    public func flatMap<T>(@noescape transform: (Self.Generator.Element) throws -> T?) rethrows -> [T]
}

try? ... returns nil if the call throws an error, so those elements will be omitted in the result.

A self-contained example just for demonstration purposes:

enum MyError : ErrorType {
    case DivisionByZeroError
}

func inverse(x : Double) throws -> Double {
    guard x != 0 else {
        throw MyError.DivisionByZeroError
    }
    return 1.0/x
}

let values = [ 1.0, 2.0, 0.0, 4.0 ]
let result = values.flatMap {
    try? inverse($0)
}
print(result) // [1.0, 0.5, 0.25]

For Swift 3, replace ErrorType by Error.

For Swift 4 use compactMap