Transforming HH:mm:SS to 'dd.MM.yy HH:mm:SS' and loosing seconds

>> time = datestr(seconds(duration),'HH:MM:SS')
time =

    '02:59:57'
>> date_and_time = datetime(time, 'ConvertFrom', 'datenum', 'Format', 'dd.MM.yy HH:mm:SS')
    
date_and_time = 
    
      datetime
    
       22.07.19 02:59:00
       

I would like to add current date to the 'time'. Why do I loose the 57 seconds when I do this transformation, and how to do it correctly?

Many thanks!

[Stephen23]

I am surprised that this does anything at all, and does not simply throw an error:

>> time = datestr(seconds(duration),'HH:MM:SS') % a date string...
>> date_and_time = datetime(time, 'ConvertFrom', 'datenum',...)
%                                                 ^^^^^^^ but here datenum!

Given that the variable time is a character vector (with a date representation), why are you telling datetime that the input is a serial date number?

More importantly, why are you converting a much better duration object to a datestring anyway? If you want a datetime object at the output then I don't see why you need any intermediate (almost) obsolete date strings or date numbers.

[Butterflyfish]

What I actually would like to do eventually is add a duration to a date and time, to get a date and time output.

E.g.

22.07.19 14:30 + 5400 seconds = 22.07.19 16:00

I thus wanted to formation the duration to the the date to make an addition. I would love to know how to do it in an easier way!

Answer 1

[Stephen23]

"I would like to add current date to the 'time'"

Sure, that is easy, by just adding a duration object to a datetime object.

You do not write what class the very badly-named duration is, but the simplest solution is to add a duration array to the datetime object of the current time:

>> D = seconds(1375.143) % a duration object
D = 
   1375.1 secs
>> T = datetime() % a datetime object (current time)
T = 
   22-Jul-2019 13:19:37
>> X = D+T % add them together!
X = 
   22-Jul-2019 13:42:32

[Butterflyfish]

Makes much more sense indeed! Thank you!

[Steven Lord]

Stephen Cobeldick has given you a better approach. But to explain why your original approach appeared to lose the seconds, look at the table of values that you can use to create the Format for a datetime in the datetime documentation. In the Format, using the characters s or ss displays the number of whole seconds and using the characters S, SS, ... SSSSSSSSS displays the number of fractional seconds. The case of the S matters.

So you didn't actually lose the seconds, you just were displaying the 0 fractional seconds instead of the 57 whole seconds.

[Butterflyfish]

Ah, that makes even more sense, thanks for this explanation!