Subset timetable based on datetime values

Hello, I have a timetable which has datetime values incrementing in ten minute intervals over a year, e.g.:

         DateTime          BoatCount    PV
    ___________________    _________    __

    29.05.2019 10:30:00        1        0 
    29.05.2019 10:40:00        0        0 
    29.05.2019 10:50:00        0        0 
    29.05.2019 11:00:00        0        0 
    29.05.2019 11:10:00        0        0 
    29.05.2019 11:20:00        0        0 
    29.05.2019 11:30:00        0        0 
    29.05.2019 11:40:00        0        0 

I want to subset this data so I am only including values recorded in daylight hours e.g. 0600-2030. How do I subset the data by datetime values? Something like...

daylighthours=TT2(TT2.DateTime=='29/05/2019 06:00:00' : '29/05/2019 20:30:00')

but which would cycle through each day of the year

Answer 1

[Adam Danz]

Here's a demo that determines which rows of a timetable have times that are between two values.

% Create a demo timetable
TT = timetable((datetime('now') - minutes(0:248:60000))', rand(242,1));

% Get time-part (in duration format)
dur = TT.Time - dateshift(TT.Time, 'start', 'day'); 
% Define sunrise and sunset
sunrise = duration(6,30,0); % 6:00
sunset = duration(20,30,0); % 20:30
% Determine which times are between sunrise and sunset
idx = dur >= sunrise & dur <= sunset; 

% Isolate rows of timetable that are during daylight
TT(idx,:)

Note: Sunrise and sunset are not fixed every day. A better approach would be to us a vector of sunrise and sunset times the same length as the datetime column and to determine whether each row is between those associated sunrise/sunset values.

[Akira Agata]

+1

To get time-part in duration format, you can also do that using timeofday function, like:

% Get time-part (in duration format)
dur = timeofday(TT.time);

[Louise Wilson]

Hi Adam, that is a really useful point! Thank you. Should I do this vector manually or do you think there is a faster way to get these times?

[Adam Danz]

Thanks, @Akira Agata

@Louise Wilson , sunrise and sunset times not only depend on time-of-year but also on location. You could either search for and download those values or you may be able to compute them.

https://en.wikipedia.org/wiki/Sunrise_equation

Update, here's an algorithm to follow

https://edwilliams.org/sunrise_sunset_algorithm.htm

Update 2, Loren has just posted a blog where this algorithm is demonstrated within a GIF image.

https://blogs.mathworks.com/loren/2020/03/23/keep-teaching-through-distance-learning/