Subtractions between consecutive rows in a table

7 vues (au cours des 30 derniers jours)
DEYIRE UMAR
DEYIRE UMAR le 24 Sep 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);

Réponse acceptée

Peter Perkins
Peter Perkins le 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)

Plus de réponses (1)

KSSV
KSSV le 24 Sep 2018
Read about function diff. It will give you the required difference.
  2 commentaires
DEYIRE UMAR
DEYIRE UMAR le 27 Sep 2018
This function seem not to solve my problem. Does it work on tables at all?
KSSV
KSSV le 27 Sep 2018
It will.....you need to enter doubles into it.

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