How to create a time vector that is incremented between two datetime strings?

I am trying to plot local time as a function of pressure recordings but I have to manually create the time vector since my data aqcuisition system does not record the time each sample is recorded. I only have the start time so I calculated the duration of the data acquisition and then tried to increments the start time to the end time using the time sampling rate (dt). But my t outputs only a single time rather than an vector. How can I resolve this? My final plot should have an x-axis that is in HH:mm:ss.SSS format.

startTime = datetime(2023,01,10,11,22,01.700);

dt = 0.001;

duration = dt*length(data); % seconds

endTime = datetime(2023,01,10,11,22,01.700+duration);

t = [startTime:dt:endTime];

Answer 1

[Star Strider]

It would help to have some idea of what you want to do, and what ‘data’ is (and for good measure ‘data’ itself).

Try something like this —

data = (0:999).';                                               % Create Missing Variable
startTime = datetime(2023,01,10,11,22,01.700);
endTime = startTime + days(0.001*(0:size(data,1)-1)).'          % Create Column Vector

endTime = 1000×1 datetime array
   10-Jan-2023 11:22:01
   10-Jan-2023 11:23:28
   10-Jan-2023 11:24:54
   10-Jan-2023 11:26:20
   10-Jan-2023 11:27:47
   10-Jan-2023 11:29:13
   10-Jan-2023 11:30:40
   10-Jan-2023 11:32:06
   10-Jan-2023 11:33:32
   10-Jan-2023 11:34:59
   10-Jan-2023 11:36:25
   10-Jan-2023 11:37:52
   10-Jan-2023 11:39:18
   10-Jan-2023 11:40:44
   10-Jan-2023 11:42:11
   10-Jan-2023 11:43:37
   10-Jan-2023 11:45:04
   10-Jan-2023 11:46:30
   10-Jan-2023 11:47:56
   10-Jan-2023 11:49:23
   10-Jan-2023 11:50:49
   10-Jan-2023 11:52:16
   10-Jan-2023 11:53:42
   10-Jan-2023 11:55:08
   10-Jan-2023 11:56:35
   10-Jan-2023 11:58:01
   10-Jan-2023 11:59:28
   10-Jan-2023 12:00:54
   10-Jan-2023 12:02:20
   10-Jan-2023 12:03:47

EDIT — (11 Jan 2023 at 1:42)

I am not certain what you want to do, however there are several examples in the documentation section Generate Sequence of Dates and Time.

.

Answer 2

[the cyclist]

I think you intended

endTime = datetime(2023,01,10,11,22,01.700)+duration;

rather than

endTime = datetime(2023,01,10,11,22,01.700+duration);

Answer 3

[Stephen23]

"But my t outputs only a single time rather than an vector. How can I resolve this?"

Of course you can use the COLON operator (you do not need to use LINSPACE), but you do need to tell MATLAB what the units are (by default the COLON operator will assume a step size in days, not in seconds, as the documentation explains here). The easiest way to do this is to use DURATION objects to specify those times:

data = rand(1,123);
st = datetime(2023,01,10,11,22,01.700, 'Format','y-MM-dd HH:mm:ss.SSS');
dt = seconds(0.001); % make this a DURATION object.
du = dt*(numel(data)-1); % Do NOT use name DURATION.
et = st+du;
t = st:dt:et;
t(:)

ans = 123×1 datetime array
   2023-01-10 11:22:01.700
   2023-01-10 11:22:01.701
   2023-01-10 11:22:01.702
   2023-01-10 11:22:01.703
   2023-01-10 11:22:01.704
   2023-01-10 11:22:01.705
   2023-01-10 11:22:01.706
   2023-01-10 11:22:01.707
   2023-01-10 11:22:01.708
   2023-01-10 11:22:01.709
   2023-01-10 11:22:01.710
   2023-01-10 11:22:01.711
   2023-01-10 11:22:01.712
   2023-01-10 11:22:01.713
   2023-01-10 11:22:01.714
   2023-01-10 11:22:01.715
   2023-01-10 11:22:01.716
   2023-01-10 11:22:01.717
   2023-01-10 11:22:01.718
   2023-01-10 11:22:01.719
   2023-01-10 11:22:01.720
   2023-01-10 11:22:01.721
   2023-01-10 11:22:01.722
   2023-01-10 11:22:01.723
   2023-01-10 11:22:01.724
   2023-01-10 11:22:01.725
   2023-01-10 11:22:01.726
   2023-01-10 11:22:01.727
   2023-01-10 11:22:01.728
   2023-01-10 11:22:01.729

See also: https://en.wikipedia.org/wiki/Off-by-one_error#Fencepost_error

Here is an alternative, simple, numerically robust approach:

t = st+seconds(0.001)*(0:numel(data)-1); % sample times
t(:)

ans = 123×1 datetime array
   2023-01-10 11:22:01.700
   2023-01-10 11:22:01.701
   2023-01-10 11:22:01.702
   2023-01-10 11:22:01.703
   2023-01-10 11:22:01.704
   2023-01-10 11:22:01.705
   2023-01-10 11:22:01.706
   2023-01-10 11:22:01.707
   2023-01-10 11:22:01.708
   2023-01-10 11:22:01.709
   2023-01-10 11:22:01.710
   2023-01-10 11:22:01.711
   2023-01-10 11:22:01.712
   2023-01-10 11:22:01.713
   2023-01-10 11:22:01.714
   2023-01-10 11:22:01.715
   2023-01-10 11:22:01.716
   2023-01-10 11:22:01.717
   2023-01-10 11:22:01.718
   2023-01-10 11:22:01.719
   2023-01-10 11:22:01.720
   2023-01-10 11:22:01.721
   2023-01-10 11:22:01.722
   2023-01-10 11:22:01.723
   2023-01-10 11:22:01.724
   2023-01-10 11:22:01.725
   2023-01-10 11:22:01.726
   2023-01-10 11:22:01.727
   2023-01-10 11:22:01.728
   2023-01-10 11:22:01.729

"My final plot should have an x-axis that is in HH:mm:ss.SSS format. "

That might suit a DURATION object better:

tod = timeofday(t);
tod.Format = 'hh:mm:ss.SSS';
plot(tod,data)