Convert Swift 3 Function to Swift 4 - swift

Question

im struggling in converting this function to Swift 4
func buildIndex(records: [Record]) -> [[Record]] {
var g = [NSDate: [Record]]()
for e in records {
if (g[e.time] == nil) {
g[e.time] = []
}
g[e.time]!.append(e) // grouping by `time`
}
return sorted(g.keys) { (a: NSDate, b: NSDate) in
a.compare(b) == .OrderedAscending // sorting the outer array by time
}
// sorting the inner arrays by `name`
.map { sorted(g[$0]!) { $0.name < $1.name } }
}
I hope someone can help me.

Answer 1

There's a lot to clean up here. The variable names are obviously a disaster, but so is the forced unwrapping. All that can be replaced with a simple call to Dictionary.init(grouping:by:)
import Foundation
struct Record {
let time: Date
let name: String
}
func buildIndex(records: [Record]) -> Any {
return Dictionary(grouping: records, by: { $0.time })
.mapValues { $0.sorted { $0.name < $1.name} }
.sorted { (pair1, pair2) in pair1.key < pair2.key }
}

Answer 2

Try it
func buildIndex(records: [Record]) -> [[Record]] {
var g = [NSDate: [Record]]()
for e in records {
if (g[e.time] == nil) {
g[e.time] = []
}
g[e.time]!.append(e) // grouping by `time`
}
return g.keys.sorted { (a: NSDate, b: NSDate) in
a.compare(b as Date) == .orderedAscending // sorting the outer array by time
}
// sorting the inner arrays by `name`
.map { g[$0]!.sorted { $0.name < $1.name } }
}
Hope it helped you.