How can I subtract the times without considering the date in question?

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Newbie 2021-8-11

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评论： Scott MacKenzie 2021-8-12

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.

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.

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Scott MacKenzie 2021-8-11

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?

Newbie 2021-8-11

1 hour

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Answer 1

Cris LaPierre 2021-8-11

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编辑：Cris LaPierre 2021-8-11

在 MATLAB Online 中打开

Use the timeofday function.

% create vector of datetimes
date = datetime(2019,[4;4;5;5],[24;25;1;2],[4;3;2;4],[30;30;50;30],0)
date = 4×1 datetime array
   24-Apr-2019 04:30:00
   25-Apr-2019 03:30:00
   01-May-2019 02:50:00
   02-May-2019 04:30:00
% Take difference of the times.
dt = diff(timeofday(date))
dt = 3×1 duration array
   -01:00:00
   -00:40:00
    01:40:00

Use the hours function to turn hh:mm:ss into decimal hours if you want.

hours(dt)
ans = 3×1
   -1.0000
   -0.6667
    1.6667

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Newbie 2021-8-11

Thanks, this works!

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Answer 2

Scott MacKenzie 2021-8-11

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编辑：Scott MacKenzie 2021-8-11

在 MATLAB Online 中打开

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
hrs = 2.5000

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Stephen23 2021-8-12

编辑：Stephen23 2021-8-12

"what deprecated date functions are you referring to? I only used datetime and minutes in my solution."

You used DATENUM here:

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:

Scott MacKenzie 2021-8-12

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.

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