Subtractions between consecutive rows in a table
5 views (last 30 days)
Show older comments
DEYIRE UMAR
on 24 Sep 2018
Answered: Peter Perkins
on 1 Oct 2018
I need a help to obtain the differences between time values which I read alongside other data and write them to a CSV file as a table. The time values are those of MATLAB time converted into milliseconds, but what I need is the differences between them to be in the table as the time is read. That is row 3 - row2, row4 - row3, row5 - row4,.......rowend - row(end-1). I attached a CSV file where I read 30 samples. Here is the relevant segment of my code:
counter = 0;
logtime_table = table();
while(counter< 30)
Timestamp = now;
timestring = datestr(Timestamp,'HH:MM:SS.FFF');
[~,~,~,hours,minutes,seconds] = datevec(timestring);
Timestamp = 1000*(3600*hours + 60*minutes + seconds);
table_row = table(Timestamp);
logtime_table = [logtime_table; table_row];
counter = counter + 1;
end
filename = strcat('logtime_table.csv');
writetable(logtime_table, filename);
0 Comments
Accepted Answer
Peter Perkins
on 1 Oct 2018
Deyire, unless you're using a pretty old version of MATLAB, use datetime and duration instead of datestr/datenum/datevec. Also your code doesn't look like it computes time differences, it computes milliseconds since year zero. Try this:
>> t0 = datetime('now'); pause(rand); t1 = datetime('now'); >> milliseconds(t1 - t0) ans = 453.54
I suggest that in your loop, you save all the timestamps, as datetimes, and all the data at each timestamp, and then ONCE, outside the loop, create a timetable something like this:
dt = diff(timestamps); dt.Format = 's';
tt = timetable(data(2:end),'RowTimes',dt)
0 Comments
More Answers (1)
See Also
Categories
Find more on Dates and Time in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!