datetime - time only - 2016a

Hi all, hope you are doing well!

I've got a question which I'm sure is very simple to anyone with any significant matlab experience!

I'm using 2016a, and am trying to filter some measuement data based on the date and time - for example, I want to compile all daytime data and all night time data into seperate graphs.

My issue is with the datetime command. when using the line of code below, is basically returns '0' for all entries, as the timedate command is including todays date - whereas the measurement data has been taken previously.

I have a 264x1 double containing all measurement values, and a 264x1 datetime with sample times - so if anyone can think of a simpler way for me to do this it would be greatly appreciated!

Thanks in advance for any help!

daytimeyn=timedate < (datetime('06:59:00','InputFormat','HH:mm:ss'))
nightla90=la90(daytimeyn==0);

Answer 1

[Steven Lord]

Use the timeofday function defined for datetime arrays.

>> timeofday(datetime('now')) % It is 3:12 PM as I type this

ans = 
  duration

   15:12:56

Fifteen hours, twelve minutes, fifty-six seconds after midnight. Compare this against a duration, like check and see if this is between 9 AM and 5 PM:

>> is9To5 = @(t) hours(9) <= timeofday(t) & timeofday(t) <= hours(17);
>> is9To5(datetime('now')) % true as I type this

[Walter Roberson]

Another approach is

timedate - dateshift(timedate, 'start', 'day')

[andytodd.msp]

Thank you both - thats great!

Steven, I found your method easier to implement, but thanks to you both for the help!

Andy