Transformation from datetime to seconds

Hi,

I wanna do a transformation from datetime dd:MM:yyyy hh:mm:ss to seconds form a table.

this is my code (not the whole)

% Specify variable properties
opts = setvaropts(opts, "TimeAbs", "InputFormat", "dd.MM.yyyy HH:mm:ss");

% Import the data
tbl = readtable("Data.xlsx", opts);

%% Prepare data for calculations
TimeAbs = tbl.TimeAbs;
t = tbl.TimeRel; % [s]

I wanna make a vector TimeRel from the TimeAbs table

Thank you for your help

Answer 1

[Adam Danz]

> I wanna do a transformation from datetime dd:MM:yyyy hh:mm:ss to seconds from a table

See a table of format identifies in the documentation

https://www.mathworks.com/help/matlab/ref/datetime.html#buhzxmk-1-Format

It's not clear whether you want to merely change the format to seconds or compute the difference and show that in seconds. I've shown both below.

TimeAbs = datetime(22,1,1,2,3,20,'Format','dd.MM.yyyy HH:mm:ss')+seconds(1:10)'

TimeAbs = 10×1 datetime array
   01.01.0022 02:03:21
   01.01.0022 02:03:22
   01.01.0022 02:03:23
   01.01.0022 02:03:24
   01.01.0022 02:03:25
   01.01.0022 02:03:26
   01.01.0022 02:03:27
   01.01.0022 02:03:28
   01.01.0022 02:03:29
   01.01.0022 02:03:30

TimeAbsSeconds = datetime(TimeAbs,'Format','ss.S')

TimeAbsSeconds = 10×1 datetime array
   21.0
   22.0
   23.0
   24.0
   25.0
   26.0
   27.0
   28.0
   29.0
   30.0

TimeAbsDiff = diff(TimeAbs)

TimeAbsDiff = 9×1 duration array
   00:00:01
   00:00:01
   00:00:01
   00:00:01
   00:00:01
   00:00:01
   00:00:01
   00:00:01
   00:00:01

seconds(TimeAbsDiff)

ans = 9×1

1 1 1 1 1 1 1 1 1

[Peter Perkins]

Or even TimeAbs.Second to get the second component of the timestamps.

Cognator, to "transform to seconds", you have to say, "seconds from where?"

Answer 2

[Steven Lord]

How do you want to perform this transformation? What does right now translate to in seconds?

N = datetime('now')

N = datetime
   31-Mar-2023 13:46:55

Do you want to calculate the number of seconds since some fixed time that the datetime occurred?

midnight = datetime(2023, 3, 31) % or

midnight = datetime
   31-Mar-2023

midnight = dateshift(N, 'start', 'day')

midnight = datetime
   31-Mar-2023

We can create a duration that represents how long elapsed between midnight and now.

elapsed = N - midnight

elapsed = duration
   13:46:55

If you need the number of seconds you can call seconds or (if you want to keep it a duration but change how it's presented) change the duration's Format property.

elapsedSeconds = seconds(elapsed) % or

elapsedSeconds = 4.9616e+04

elapsed.Format = 's' % Just change the format

elapsed = duration
   49616 sec

As I type this elapsed is about 13 and 3/4 hours and elapsedSeconds is close to 50,000. Does that make sense?

estimate = 13.75*60*60 % 13.75 hours * 60 minutes/hour * 60 seconds/minute = units of seconds

estimate = 49500

That looks like reasonably close to the value I received in elapsed and elapsedSeconds.