Convert UNIX NanoSeconds to DTG in Milliseconds

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Timothy
Timothy 2023-8-18
回答： dpb 2023-8-19
Hello,
I have to do 2 things: convert UNIX nanoseconds to DTG Nanoseconds, and then convert DTG Nanoseconds to DTG Milliseconds. The second conversion would be a "SUM" of all the entries into one millisecond. So for every nanosecond entry within millisecond "1," I would like to sum the different parts of the table and add them together to create a millisecond register instead of a nanosecond register. Does this make sense? Any questions are welcomed in order to reach this goal!
Thanks,
Tim
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Timothy
Timothy 2023-8-19
Now that I have it in Date-Time with nanoseconds, any ideas how to simply round it off to milliseconds?
Walter Roberson
Walter Roberson 2023-8-19
If you had the time in int64 or uint64 nanoseconds, then to round to milliseconds, just divide them by 1000: operations on integer data classes automatically round
If you have double precision numbers, then see round which has the ability to indicate how many digits you want to round to.

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dpb
dpb 2023-8-19
Ah! That simplifies the problem immensely; you've already passed the hard part.
To do the initial request to sum over millisec time intervals, turn the data table into a timetable and use retime with the 'regular' sample rate and @sum method...
tt=timetable(yourdatetimevar,restofdata);
ttMS=retime(tt,'regular','sum','SampleRate',1000); % aggregate a msec sample rate
The above will start at the actual time in msec and aggreate within those groups; it will not resample to approximate at even msec times. If want that, use retime() and interpolate first, then aggregate. There may be a way to do both in one step, I'm not sure.

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