Rounding Time to next half hour

I have time stamps at one second increments (9/8/2015 14:31:01, 9/8/2015 14:31:02, 9/8/2015 14:31:03...) that I would like to round up to the next half hour. So 9/8/2015 14:31:01 would be 9/8/2015 15:00:00 9/8/2015 14:29:01 would be 9/8/2015 14:30:00 and so on. Is there something similar to Excel's ceiling function where I can specify to what fraction I want to round up to?

Answer 1

[Star Strider]

This is probably more efficient than it looks:

tv = ['9/8/2015 14:28:01'; '9/8/2015 14:29:01'; '9/8/2015 14:31:01'; '9/8/2015 14:31:02'; '9/8/2015 14:31:03'];
tv_dv = datevec(datenum(tv, 'mm/dd/yyyy HH:MM:SS'));            % Generate ‘datevec’ Date Vectors
tv_rnd = datevec(datenum([tv_dv(:,1:4) [30*(tv_dv(:,5)<30) + 60*(tv_dv(:,5)>=30)] tv_dv(:,6)]));    % Rounded Date Vectors

It uses the logic of the vector ‘[30*(tv_dv(:,5)<30) + 60*(tv_dv(:,5)>=30)]’ to brute-force round all minute values less than 30 to 30, and everything greater than 30 to 60. I let the logic of the datenum function take care of conversion, and then converted them back into date vectors (so I could check the result).

Remove the datevec call in tv_rnd to keep them as date numbers, or convert them back to date strings instead in your code.

Answer 2

[Peter Perkins]

In MATLAB R2014b or later:

>> d1 = datetime({'9/8/2015 14:31:01', '9/8/2015 14:31:02', '9/8/2015 14:31:03'})
d1 = 
   08-Sep-2015 14:31:01   08-Sep-2015 14:31:02   08-Sep-2015 14:31:03
>> d2 = dateshift(d1,'start','hour') + minutes(30)
d2 = 
   08-Sep-2015 14:30:00   08-Sep-2015 14:30:00   08-Sep-2015 14:30:00

[Trung Hieu Le]

Hi Peter,

Could you help me revise the code to receive the rounding time to next half hour as my required output?

    >> d1 = datetime({'9/8/2015 14:46:01'})
My required output:
   08-Sep-2015 15:00:00

If I use your code:

    >> d2 = dateshift(d1,'start','hour') + minutes(30)

The result will be 14:30:00.

If I revise the code:

    d2 = dateshift(d1,'start','hour') + minutes(60)

I will receive the right answer, however, do you know which code will be automatically for this?

Thanks!