How can I subtract the times without considering the date in question?
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I have a vector of time which are linked to dates but I only want to subtract the times from each other without considering the dates too. For example, I want to do 4:30 - 3:30 is equal to 1 hour and then 3:30 - 2:50 is equal to 40 minutes (0.6666667) and etc. I dont want Matlab to consider the date period basically.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/709257/image.jpeg)
I have this code for the time from 25-Apr to 01-May but it does take into account the date too:
out1m=24-(seconds(diff(datetime([T_Smooth{2,4};T_Smooth{3,4}])))/3600);
Can anyone help please? Thank you.
2 Comments
Scott MacKenzie
on 11 Aug 2021
Just to clarify... What result do you expect if you subtract 3:30 on April 26 from 4:30 on April 27? 1 hour or 25 hours?
Accepted Answer
Cris LaPierre
on 11 Aug 2021
Edited: Cris LaPierre
on 11 Aug 2021
% create vector of datetimes
date = datetime(2019,[4;4;5;5],[24;25;1;2],[4;3;2;4],[30;30;50;30],0)
% Take difference of the times.
dt = diff(timeofday(date))
Use the hours function to turn hh:mm:ss into decimal hours if you want.
hours(dt)
More Answers (1)
Scott MacKenzie
on 11 Aug 2021
Edited: Scott MacKenzie
on 11 Aug 2021
Here's one way to do this:
% test data (one month in 30-min increments)
dt = datetime(2021,4,1):minutes(30):datetime(2021,5,1);
% indices of datetime elements to compute hour difference between
n1 = 154;
n2 = 255;
x = datenum(dt(n2) - dt(n1));
hrs = rem(x,1) * 24
5 Comments
Stephen23
on 12 Aug 2021
Edited: Stephen23
on 12 Aug 2021
"what deprecated date functions are you referring to? I only used datetime and minutes in my solution."
You used DATENUM here:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/710057/image.png)
https://www.merriam-webster.com/dictionary/deprecated: "3: to withdraw official support for or discourage the use of (something, such as a software product) in favor of a newer or better alternative."
The DATENUM documentation currently contains this note:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/710062/image.png)
Scott MacKenzie
on 12 Aug 2021
Oops, yes, I used datenum as well. Thanks for pointing that out. The language to discourage use of this function could be a tad stronger, however. Below is what appears for xlsread, as an example.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/710092/image.png)
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