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I’d like to create a scheduler app that contains a...
# stdlib
n
I’d like to create a scheduler app that contains a list of events. Each event has a 
startDate
and an 
endDate
. I’d like to determine which events overlap so I can place events in a different column. Is there a way to apply some sort of 
groupBy
function to accomplish a way for me to group them?
e
overlapping ranges are not transitive so this requires a different approach than groupBy
👍 1
n
Darn. Any suggestions?
e
a
Might also be able to sort by start time and use a stack -- repurpose this interview question https://www.techiedelight.com/merging-overlapping-intervals/
👍 1
n
Oh thanks!
a
n
Thanks @andries.fc! If I have a list of these:
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data class Event(val id: Int, val startDate: LocalDate, val endDate: LocalDate, val name: String)
How would I use your function?
a
Will have a look just in the road
👍 1
@Nick here is simplification for your use case: https://gist.github.com/andriesfc/20412b74bad98d4cd98f5b374b25978a
n
❤️❤️❤️❤️❤️❤️!!!
Thanks so much.
It looks great but I'll try it out tomorrow!
a
no problem.. just make sure i've covered all the edge cases in the 
Event.overlap()
function before just using it. did not write any test cases.
e
a. would be much simpler and easier to verify if written as
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fun Event.overlap(other: Event): Boolean = startDate <= other.endDate && endDate >= other.startDate
b. there's no reason to use a fold,
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val overlappingEvents = buildList {
    for (event in events) // ...
}
c. the approach is just wrong,
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val events = listOf(
    Event(1, LocalDate("2022-04-20"), LocalDate("2022-04-23"), "event-1"),
    Event(2, LocalDate("2022-04-20"), LocalDate("2022-04-21"), "event-2"),
    Event(3, LocalDate("2022-04-22"), LocalDate("2022-04-23"), "event-3"),
).sortedBy(Event::startDate)
returns two disjoint groups instead of one
it's not that hard to borrow from a naïve interval tree and simplify (assuming you only need to build the overlapping structure once, not add or make queries later on), https://pl.kotl.in/gygTr_6x3. but if you want to be able to add and remove events dynamically, you really do need a proper interval tree implementation
❤️ 1
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