Week in year
[N] = weeknum(D, W, E)
Serial date number or a date string.
(Optional) A numeric representation of the day a week begins. The week start values and their corresponding day are:
(Optional) Indicates if the week of the year display is in the European standard. The European standard considers first week of year to be first week longer than 3 days, offset by the given week's start day. Set to 1 to use the European standard. The default setting is 0.
[N] = weeknum(D, W, E) returns the week of the year given D, a serial date number or a date string, W, a numeric representation of the day a week begins, and when E is set to 1, the week of the year is in the European standard.
The weeknum function considers the week containing January 1 to be the first week of the year.
You can determine the week of the year using a serial date number
N = weeknum(728647)
N = 52
or a date string
N = weeknum('19-Dec-1994')
N = 52
The first week of the year must have at least 4 days in it. For example, January 8, 2004 was a Thursday.
ans = 2
You can use weeknum with datenum:
ans = 1 1 1 2 2 2 2 2
The default start day of the week is Sunday. Every day after, and including the first Sunday of the year (04-Jan-2004), returns 2 denoting the second week. In this case, the first of week of the year started before January 1, 2004.
You can also use weeknum with datenum and specify a W value of 5 to indicate that the weeks start on Thursday:
ans = 1 1 1 1 1 1 1 2
The first week of the year that has 4 or more days, based on the specified start day, is considered week one (even if this isn't the first week in the calendar). Any day falling in (or before) this week is given a week number of 1.