functional.swift

import UIKit

typealias Session = (NSDate, [Int])

let data = [
    ["created": NSDate(timeIntervalSince1970: 1422600001), "reps": 0],
    ["created": NSDate(timeIntervalSince1970: 1422600002), "reps": 1],
    ["created": NSDate(timeIntervalSince1970: 1422600003), "reps": 1],
    ["created": NSDate(timeIntervalSince1970: 1422700000), "reps": 0],
    ["created": NSDate(timeIntervalSince1970: 1422700000), "reps": 0],
]

func distinct<T: Equatable>(source: [T]) -> [T] {
    var unique = [T]()
    for item in source {
        if !contains(unique, item) {
            unique.append(item)
        }
    }
    return unique
}

func buildIndex(records: [[String: NSObject]]) -> [Session] {

    func getDate(date: NSDate) -> NSDate {
        let formatter = NSDateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"

        let newDate = formatter.stringFromDate(date)
        return formatter.dateFromString(newDate)!
    }

    let dates = distinct(records.map { getDate($0["created"] as NSDate) })

    return dates.map { (date) -> Session in
        let forDate = records.filter { date == getDate($0["created"] as NSDate) }
        return (date, forDate.map { $0["reps"] as Int })
    }
}

let days = buildIndex(data)

for (day, reps) in days {
    println(day)

    for rep in reps {
        println(rep)
    }
}

imperative.swift

import UIKit

typealias Session = (NSDate, [Int])

let data = [
    ["created": NSDate(timeIntervalSince1970: 1422600000), "reps": 0],
    ["created": NSDate(timeIntervalSince1970: 1422600000), "reps": 1],
    ["created": NSDate(timeIntervalSince1970: 1422600000), "reps": 1],
    ["created": NSDate(timeIntervalSince1970: 1422700000), "reps": 0],
    ["created": NSDate(timeIntervalSince1970: 1422700000), "reps": 0],
]

func buildIndex(records: [[String: NSObject]]) -> [Session] {
    var result = [Session]()
    var dates = [NSDate]()

    // Seperate out all the dates
    for rec in records {
        let date = rec["created"] as NSDate
        if !contains(dates, date) {
            dates.append(date)
        }
    }

    // Find all the reps for each date
    for date in dates {
        var repsForDate = [Int]()

        for rec in records {
            let created = rec["created"] as NSDate

            if created == date {
                let reps = rec["reps"] as Int
                repsForDate.append(reps)
            }
        }

        result.append((date, repsForDate))
    }

    // Return results
    return result
}

let days = buildIndex(data)

// Looping over all the days returns the day and the reps
for (day, reps) in days {
    println(day)

    for rep in reps {
        println(rep)
    }
}