sorted(by:)

Part of the Logic & Flow section of Coddy's Swift journey. Lesson 30 of 56.

You've used .sorted() on arrays of Comparable values like numbers or strings. When you want to sort by something else, supply a closure that takes two elements and returns true when the first should come before the second.

let words = ["banana", "hi", "hello"]
let byLength = words.sorted { $0.count < $1.count }
print(byLength)              // ["hi", "hello", "banana"]

For descending order, swap the comparison:

let down = words.sorted { $0.count > $1.count }
print(down)                  // ["banana", "hello", "hi"]

The closure can compare any derived value, length, last letter, an entry in a hash. Whatever the closure compares decides the sort.

min(by:) and max(by:) work the same way but return a single optional element rather than a sorted copy.

Challenge

Medium

Read a single line of input: a comma-separated list of name:age pairs.

Print three lines:

Names sorted by age ascending, joined with ,. Break ties by sorting the tied names alphabetically.
The name of the oldest person (use max(by:)). On a tie, the one that appears first wins.
The name of the youngest person (use min(by:)). On a tie, the one that appears first wins.

For input alice:30,bob:22,cara:30,dan:18, the output is:

dan,bob,alice,cara
alice
dan

Try it yourself

let people = readLine()!.components(separatedBy: ",").map { pair -> (String, Int) in
    let parts = pair.components(separatedBy: ":")
    return (parts[0], Int(parts[1])!)
}

// TODO: sort by age asc (tiebreak by name); max(by:) for oldest; min(by:) for youngest