How do I sort date components in Swift? - ios

Question

I want to group data by dates which has initial format of yyyy-MM-dd'T'HH:mm:ss.SSSZ and display as E, dd MMM. I have managed to group them by the dates but failed to sort the dates in a descending order. How do I sort the date components after grouping in Dictionary?
JSON Response
{
"list": [
{
"userId": "test1",
"transactionTime": "2019-06-20T14:01:00.253+08:00"
},
{
"userId": "test2",
"transactionTime": "2019-06-16T14:02:00.253+08:00"
},
{
"userId": "test3",
"transactionTime": "2019-06-12T14:01:00.253+08:00"
},
{
"userId": "tes4",
"transactionTime": "2019-06-17T14:02:00.253+08:00"
},
]
}
Grouping
func convertToDateObj() -> Date {
let dateFormatter = DateFormatter()
// Convert from initial date string to date object
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
let dateObj = dateFormatter.date(from: self)!
return dateObj
}
// Group list by date
let groupedList = Dictionary(grouping: rawTransactionsList, by: { list -> DateComponents in
let dateObj = list.transactionTime.convertToDateObj()
let date = Calendar.current.dateComponents([.day, .month], from: (dateObj))
return date
})
// QUESTION
// How do I sort the keys?
// groupList.keys.sorted(...)?
// Populate my list with grouped list
groupedList.keys.forEach { key in
print("Group keys \(key)")
let values = groupedList[key]
groupedtransactionsList.append(values ?? [])
}

Answer 1

You should probably also group by the year, otherwise the same day in different years will be in the same group:
let date = Calendar.current.dateComponents([.day, .month, .year], from: (dateObj))
One way to sort the keys is to convert the date components back into Dates, using Calendar.current.date(from:):
let sortedList = groupedList.sorted {
Calendar.current.date(from: $0.key) ?? Date.distantFuture <
Calendar.current.date(from: $1.key) ?? Date.distantFuture
}
sortedList.forEach { key, values in
print("Group keys \(key)")
groupedtransactionsList.append(values ?? [])
}

Answer 2

My suggestion is to use a date string with format yyyy-MM-dd as dictionary key rather than date components. This string can be sorted.
let groupedList = Dictionary(grouping: rawTransactionsList, by: { list -> String in
let dateObj = list.transactionTime.convertToDateObj()
let comps = Calendar.current.dateComponents([.day, .month, .year], from: dateObj)
return String(format: "%ld-%.2ld-%.2ld", comps.year!, comps.month!, comps.day!)
})
groupedtransactionsList = groupedList.keys.sorted(by: >).map { groupedList[$0]! }