Convert older Date to current Date with old time

Ignition
1

Is there anyway to convert say Dec 12 08:26:03 EST 2023 to the current Date with the old time (Dec 18 08:26:03 EST 2023)??

2

Yes there is.
Where are you trying to do this? In an expression or in a script?

3

A script

4

Something like this should work:

daysDiff = system.date.daysBetween(date1, date2)
newDate = system.date.addDays(date1, daysDiff)
5

What if I do not know that date2, for example if I have date1 = DEC 12 8:26:03 - I want to dynamically turn that into DEC 18 8:26:03 - I do not have DEC 18 8:26:03

6 
inBetween = system.date.minutesBetween(last_sample_time, system.date.now())
next_sample_time = system.date.addMinutes(last_sample_time, inBetween)

this would end up comparing to the current date and give me a result that is not accurate

7

Why are you calculating in minutes? Calculate in days.
You can use the system.date.midnight() function if you want to bring both dates to midnight before calculating daysBetween.

1 Like
8 
system.date.setTime(
    system.date.now(),
    system.date.getHour24(last_sample_time),
    system.date.getMinute(last_sample_time),
    system.date.getSecond(last_sample_time)
)

https://docs.inductiveautomation.com/display/DOC81/system.date.setTime

https://docs.inductiveautomation.com/pages/viewpage.action?pageId=58603995

1 Like
9

Ah!

inBetween = system.date.daysBetween(system.date.midnight(last_sample_time), system.date.midnight(system.date.now()))
next_sample_time = system.date.addDays(last_sample_time, inBetween)

This should achieve what I want. Does this work for the edge case of it being AM or PM ?

10

Would this be a better solution for the edge cases of daylight savings, different month lengths, time zone changes ???

11

I would expect there to be less "surprises" with the setTime approach - it's going to give you the time you "expect" with the given algorithm. Subtracting days may have DST/timezone complications. In general, though, date math is complicated, and there is no single perfect solution. You're always leaving something off the table.

2 Likes
12

Thanks! @PGriffith and @Transistor