NWEEKINYEAR

NWEEKINYEAR(x;s) number of the week through the year for date-time value x. The default setting for s is 'iso'; this uses the definition of ISO Standard IS-8601 (1988) in which any week (starting on Monday) that lies in more than one year is assigned a week number for the year in which most of its days occur. The alternative setting, 'simple', takes the first week of the year as the one containing 1st January.