# calculate week of year

20 views (last 30 days)
Richard on 18 Dec 2012
Commented: Erik Johannes Loo on 25 Oct 2021
I have an annual time series where measurements are recorded at hourly intervals:
StartDate = '2011-01-01 00:00';
EndDate = '2011-12-031 23:00';
DateTime=datevec(datenum(StartDate,'yyyy-mm-dd HH:MM'):60/(60*24):...
datenum(EndDate,'yyyy-mm-dd HH:MM'));
dat = 2+(20-2).*rand(size(DateTime,1),1);
I would like to calculate the mean 24 hour cycle for each week of the year i.e. for week 1, day of year 1 to 7 I want to calculate the average 00:00, 01:00,... and so on so eventually I will end up with 52, 24 hour series i.e. one for each week of the year. Matlab does have a function called 'weeknum' which returns the week number from a given seriel date number, however, this function is in the financial toolbox. Can anyone suggest an alternative methdo for finding week number?

Jan on 18 Dec 2012
function weekOfYear = yourWeekNum(s)
% Get 1st of January of the year:
v = datevec(s);
v1 = v;
v1(:, 2:3) = 1;
v1(:, 4:6) = 0;
s1 = datenum(v1);
dayOfYear = s - s1;
weekOfYear = floor(dayOfYear / 7) + 1;
Please check this, because it is written in the editor and not tested.
##### 2 CommentsShowHide 1 older comment
DWag on 27 Mar 2020
Yes it's great! And just a note for whoever uses it in the future, choose a date and double-check it to make sure it rounds to your needs. I rounded up isntead of having partial days.

Steven Lord on 27 Mar 2020
Since the original question was written, we introduced datetime. If you're representing your time and date data as a datetime, call week on your datetime with 'weekofyear' as the weekType input.
##### 2 CommentsShowHide 1 older comment
Erik Johannes Loo on 25 Oct 2021
I will suggest something that I am not 100% sure it is correct - but I also haven't found satisfactory answers elsewhere:
sum(weekday(dateshift(inputDate, 'start', 'year'):dateshift(inputDate, 'end', 'week')) == 5)
This snippet basically counts the no. of Thursdays up to and including the week of the input date and should satisfy the ISO standard definition that the first week is (as per Wikipedia):
• the week with the starting year's first Thursday in it (the formal ISO definition)

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