====== Week of the Year (Expression Function) ======

===== Purpose =====
The **Week of the Year** function (WEEK_OF_THE_YEAR) generates a number that represents the week of the year as defined by the ISO-8601 standard format for a timestamp provided in a given timezone. 

{{:week_of_the_year_initial.png?direct&600|}}

===== Parameters =====
The **Week of the Year** function has two parameters, one of which is required:

==== Timestamp ====

Allowed Inputs: [[Field|field]] value or a number representing a Unix timestamp.

There are several sources of Unix timestamps available.  For example the stored value of a [[Field Type - Date|date]] or [[Field Type - Date Time| date time]] field is a Unix timestamp.  Also When using the advanced interface the output of the [[Expression Function - Date|date]] or [[Expression Function - Date and Time| date time]] expression function is a Unix timestamp.

==== Timezone ====

Allowed Inputs: [[Field|field]] value or a text string

The second optional parameter of the **Week of the Year** function is a string that represents the timezone.  Either use the  query builder to choose a field that contains the value or use type a value to enter a number.  The value should be based on the tz (timezone) database used by Linux and other Unix system in the form “Area/Location” e.g. "America/New_York".  If no value is provided then the current user's timezone is used.

===== Output =====

The output of the **Week of the Year** function is number representing the week of the year as defined by the ISO-8601 where weeks start on monday.
===== Example =====

Because weeks my cross year boundries then it is possible for a day to return a week number based on the next or previous calendar year.  December 31, 2012 is a Monday and therefor is considered part of the first week of 2013 for example WEEK_OF_THE_YEAR(1357009728,"America/New_York") will return "01". December 30, 2012 is a Sunday so it is part of the last week of 2012 and WEEK_OF_THE_YEAR(1356923807,"America/New_York") will return "52".