Objective C Solution
NSArray * array = @[@"1", @"2", @"3"];
NSString * stringFromArray = [[array valueForKey:@"description"] componentsJoinedByString:@"-"]; // "1-2-3"
Those who are looking for a solution in Swift
If the array contains strings, you can use the String's join method:
var array = ["1", "2", "3"]
let stringFromArray = "-".join(array) // "1-2-3"
In Swift 2:
var array = ["1", "2", "3"]
let stringFromArray = array.joinWithSeparator("-") // "1-2-3"
In Swift 3 & 4
var array = ["1", "2", "3"]
let stringFromArray = array.joined(separator: "-") // "1-2-3"