Summing Datenum resets after 24 hours

Hello all,

I am trying to sum datenum values, and return them to hours:mins:secs format when all complete. When the amount of time is relatively small, it works as expected, but once it rolls past 24 hours, it resets.

Example:

a = datenum('21:10:00','hh:MM:ss')
b = datenum('1:10:00','hh:MM:ss')
c = datestr(x+y,'hh:MM:ss')
c = '22:20:00'

x = datenum('21:10:00','hh:MM:ss')
y = datenum('7:10:00','hh:MM:ss')
z = datestr(x+y,'hh:MM:ss')
z = '04:20:00'

Anyone know how to get around that to output :

z = '28:10:00'

and also 3 digit hours if need-be.

Any help is greatly appreciated!

Answer 1

[Stephen23]

As Steven Lord wrote, serial date numbers are not the right tool for the task: amongst other things you will struggle against defining an appropriate pivot year (which is essential for the task that you are attempting) and as you have already found DATESTR will (by design) return the hours of a day, not an arbitrarily increasing hour count.

But you can easily do it yourself without serial date numbers, here using time in seconds:

v = [60*60,60,1];
a = v * sscanf('21:10:00','%d:%d:%d'); % seconds
b = v * sscanf( '1:10:00','%d:%d:%d'); % seconds
mytime(a+b)

ans = '22:20:00'

x = v * sscanf('21:10:00','%d:%d:%d'); % seconds
y = v * sscanf( '7:10:00','%d:%d:%d'); % seconds
mytime(x+y)

ans = '28:20:00'

where:

function str = mytime(tmp)
spl = nan(1,3);
spl(3) = mod(tmp,60); % seconds
tmp    = fix(tmp/60);
spl(2) = mod(tmp,60); % minutes
tmp    = fix(tmp/60);
spl(1) =     tmp    ; % hours
str = sprintf('%02d:%02d:%02d',spl);
end

[Ruger28]

Perfect, this is exactly what I need. Thank you very much for your help!

[Steven Lord]

Instead of using sscanf you could directly call duration as of release R2018a. I know this doesn't help the original poster, but I'm including it as an FYI.

d = duration('21:10:00', 'InputFormat', 'hh:mm:ss')

d = duration
   21:10:00

Answer 2

[Matt Gaidica]

I don't know if the datetime functions are going to allow that triple digit hour. Here's one approach.

z = sprintf('%03i:%02i:%02i',hour(x) + hour(y), minute(x+y), second(x+y))

[Ruger28]

thanks, I'll give this a go and report back!

[Ruger28]

Update: the tiem commands are also not available in 2014a. Thanks again, though.

Answer 3

[Steven Lord]

Serial date numbers are not the right tool for this job. You want to use a duration array.

dur1 = duration(12, 23, 45)

dur1 = duration
   12:23:45

dur2 = hours(67)+minutes(89)

dur2 = duration
   68.483 hr

D = dur1 + dur2

D = duration
   80:52:45

If you want you can control the display Format.

D.Format = 'h'

D = duration
   80.879 hr

[Ruger28]

Thank you for your reply, but I am using 2014a, and duration was introduced in 2014b, unfortunately.