Get array of dates from an array of dates - ios

Question

I have an array of Date objects like the following example:
let dates = [date1, date2, date3, date4, date5]
How can I create subarrays for dates that have the same day of month, month and year.
Example:
date1 = 20/04/2020
date2 = 19/04/2020
date3 = 19/04/2020
date4 = 18/04/2020
date5 = 18/04/2020
...
With this I wanted the following:
let group1 = [date1]
let group2 = [date2, date3]
let group3 = [date4, date5]
let group4 = //...
I have tried DateComponents and .map, .filter, etc functions but somehow I cannot do this.
Can I get a hint?
thanks.

Answer 1

The code extracts the date components for year, month and day from each date and groups by them and then maps the values from the grouped result to an array of arrays per date. To be able to have the original dates in the end result a tuple is used as value type for the dictionary
let groupedDates = Dictionary(grouping: dates
.map { ($0,Calendar.current.dateComponents([.year, .month, .day], from: $0))}, by: {$0.1})
.mapValues {value in value.map {$0.0}}
.values

Answer 2

Just create structure that tracks the year, month, and day.
struct DateCluster {
let day: Int
let month: Int
let year: Int
var dates: [Date] = []
init(date: Date) {
let cal = Calendar.current
day = cal.component(.day, from: date)
month = cal.component(.month, from: date)
year = cal.component(.year, from: date)
dates.append(date)
}
func doesDateBelong(_ date: Date) -> Bool {
let cal = Calendar.current
return cal.component(.day, from: date) == day
&& cal.component(.month, from: date) == month
&& cal.component(.year, from: date) == year
}
}
And here's the usage:
func makeDate(year: Int, month: Int, day: Int) -> Date? {
let cal = Calendar.current
let components = DateComponents(year: year, month: month, day: day)
return cal.date(from: components)
}
var clusters: [DateCluster] = []
var dates = [
makeDate(year: 2020, month: 4, day: 20),
makeDate(year: 2020, month: 4, day: 19),
makeDate(year: 2020, month: 4, day: 19),
makeDate(year: 2020, month: 4, day: 18),
makeDate(year: 2020, month: 4, day: 18),
].compactMap { $0 }
for date in dates {
if let index = clusters.firstIndex(where: { $0.doesDateBelong(date) }) {
clusters[index].dates.append(date)
} else {
clusters.append(.init(date: date))
}
}
The result below will be an array of an array of dates all grouped by year, month, and day.
let groupedDates = clusters.map { $0.dates }