sorting dates if timestamp is greater than zero - swift

Question

I'm trying to sort dates from oldest to most recent but I want timestamps that are zero to be at the bottom of the sorted list. Only dates that are greater than zero should be sorted and at the top of the list.
The issue I have is that timestamps that are zero show up at the top... how do I ignore zero timestamps and put them at the bottom and give the timestamps that are greater > 0 priority on the list ?
Here's what I have:
//DATE SORT
self.tasklist.sort { $0.onsiteThreshold < $1.onsiteThreshold }
self.tasklist.sort { $0.resolutionThreshold < $1.resolutionThreshold }
self.tasklist.sort { $0.scheduleDateTime < $1.scheduleDateTime }
self.tasklist.sort { (o1, o2) -> Bool in
if o1.onsiteThreshold == 0 || o2.onsiteThreshold == 0 || o1.resolutionThreshold == 0 || o2.resolutionThreshold == 0 || o1.scheduleDateTime == 0 || o2.scheduleDateTime == 0 {
return false
}
return true
}

Answer 1

Sorting an array four(!) times is pretty expensive.
A more efficient way is first to move all items which contain zero properties to the end of the list with partition(by:). This API is part of Standard Library but doesn't preserve the order of the left side, therefore the partition must take place first.
let partitionIndex = tasklist.partition(by: {$0.onsiteThreshold == 0 || $0.resolutionThreshold == 0 || $0.scheduleDateTime == 0})
Then sort the left side tasklist[0..<partitionIndex] by all three properties and append the right side.
let sorted = tasklist[0..<partitionIndex].sorted { (lhs, rhs) in
if lhs.scheduleDateTime == rhs.scheduleDateTime {
if lhs.resolutionThreshold == rhs.resolutionThreshold {
return lhs.onsiteThreshold < rhs.onsiteThreshold
}
return lhs.resolutionThreshold < rhs.resolutionThreshold
}
return lhs.scheduleDateTime < rhs.scheduleDateTime
}
taskList = sorted + tasklist[partitionIndex...]