Kotlin - Sort List by using formatted date string (functional)
Another alternative to the excellent Saravana answer (for minimalist and compact freaks like me..) is:
val cmp = compareBy<String> { LocalDateTime.parse(it, DateTimeFormatter.ofPattern("dd-MM-yyyy | HH:mm")) }
list.sortedWith(cmp).forEach(::println)
01-08-2015 | 09:29
14-10-2016 | 15:48
15-11-2016 | 19:43
Ps: it
is the default variable for single inputs
More than one approach can be used. It depends on how you process after you get the sorted result.
Points to note:
java.time.LocalDateTime
has already implementedjava.lang.Comparable<T>
Interface. We can use the kotlin stdlibList.sortBy
to sort theList<LocalDateTime>
directly.
Ref:
// https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sorted-by.html
fun <T, R : Comparable<R>> Iterable<T>.sortedBy(
selector: (T) -> R?
): List<T>
The easiest way is to transform the String -> java.time.LocalDateTime
and use the List.sortBy
directly.
The whole implementation could be like this:
import java.time.LocalDateTime
import java.time.format.DateTimeFormatter
...
// Create a convert function, String -> LocalDateTime
val dateTimeStrToLocalDateTime: (String) -> LocalDateTime = {
LocalDateTime.parse(it, DateTimeFormatter.ofPattern("dd-MM-yyyy | HH:mm"))
}
val list = listOf("14-10-2016 | 15:48",
"01-08-2015 | 09:29",
"15-11-2016 | 19:43")
// You will get List<LocalDateTime> sorted in ascending order
list.map(dateTimeStrToLocalDateTime).sorted()
// You will get List<LocalDateTime> sorted in descending order
list.map(dateTimeStrToLocalDateTime).sortedDescending()
// You will get List<String> which is sorted in ascending order
list.sortedBy(dateTimeStrToLocalDateTime)
// You will get List<String> which is sorted in descending order
list.sortedByDescending(dateTimeStrToLocalDateTime)
If you want to use org.joda.time.DateTime
, you can just make a tiny change on the convert function.
A friendly reminder, always pick val
as your first choice in Kotlin :).