Real life map+reduce solution

gistfile1.swift

//
// returns the list of different extensions from a bunch of files
//
func differentExtensions(fileNames: [String]) {
	
	// Step 1. Map: process file names list to convert to extensions list
	let allExtensions = fileNames.map { $0.pathExtension.lowercaseString }

	// Step 2. Reduce: iterate removing duplicates
	return allExtensions.reduce([String]()) { (acum, value) -> [String] in
		// use filter here to find whether or not it already exists
		if (acum.filter() { return $0 == value }).isEmpty {
			return acum + [value]
		}

		return acum
	}
}