WEEK Function

Returns the week-number value.
Category: Date and Time

Syntax

WEEK(<sas-date> , <'descriptor'> )

Optional Arguments

sas-date
specifies the SAS data value. If the sas-date argument is not specified, the WEEK function returns the week-number value of the current date.
descriptor
specifies the value of the descriptor. The following descriptors can be specified in uppercase or lowercase characters.
U (default)
specifies the number-of-the-week within the year. Sunday is considered the first day of the week. The number-of-the-week value is represented as a decimal number in the range 0–53. Week 53 has no special meaning. The value of week('31dec2006'd, 'u') is 53.
Tip:The U and W descriptors are similar, except that the U descriptor considers Sunday as the first day of the week, and the W descriptor considers Monday as the first day of the week.
V
specifies the number-of-the-week whose value is represented as a decimal number in the range 1–53. Monday is considered the first day of the week and week 1 of the year is the week that includes both January 4th and the first Thursday of the year. If the first Monday of January is the 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year.
W
specifies the number-of-the-week within the year. Monday is considered the first day of the week. The number-of-the-week value is represented as a decimal number in the range 0–53. Week 53 has no special meaning. The value of week('31dec2006'd, 'w') is 53.
Tip:The U and W descriptors are similar except that the U descriptor considers Sunday as the first day of the week, and the W descriptor considers Monday as the first day of the week.

Details

The Basics

The WEEK function reads a SAS date value and returns the week number. The WEEK function is not dependent on locale, and uses only the Gregorian calendar in its computations.

The U Descriptor

The WEEK function with the U descriptor reads a SAS date value and returns the number of the week within the year. The number-of-the-week value is represented as a decimal number in the range 0–53, with a leading zero and maximum value of 53. Week 0 means that the first day of the week occurs in the preceding year. The fifth week of the year is represented as 05.
Sunday is considered the first day of the week. For example, the value of week('01jan2007'd, 'u') is 0.

The V Descriptor

The WEEK function with the V descriptor reads a SAS date value and returns the week number. The number-of-the-week is represented as a decimal number in the range 01–53. The decimal number has a leading zero and a maximum value of 53. Weeks begin on a Monday, and week 1 of the year is the week that includes both January 4th and the first Thursday of the year. If the first Monday of January is the 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year. In the following example, 01jan2006 and 30dec2005 occur in the same week. The first day (Monday) of that week is 26dec2005. Therefore, week('01jan2006'd, 'v') and week('30dec2005'd, 'v') both return a value of 52. This means that both dates occur in week 52 of the year 2005.

The W Descriptor

The WEEK function with the W descriptor reads a SAS date value and returns the number of the week within the year. The number-of-the-week value is represented as a decimal number in the range 0–53, with a leading zero and maximum value of 53. Week 0 means that the first day of the week occurs in the preceding year. The fifth week of the year would be represented as 05.
Monday is considered the first day of the week. Therefore, the value of week('01jan2007'd, 'w') is 1.

Comparisons of Descriptors

U is the default descriptor. Its range is 0-53, and the first day of the week is Sunday. The V descriptor has a range of 1-53 and the first day of the week is Monday. The W descriptor has a range of 0-53 and the first day of the week is Monday.
The following list describes the descriptors and an associated week:
  • Week 0:
    U indicates the days in the current Gregorian year before week 1.
    V does not apply.
    W indicates the days in the current Gregorian year before week 1.
  • Week 1:
    U begins on the first Sunday in a Gregorian year.
    V begins on the Monday between December 29 of the previous Gregorian year and January 4 of the current Gregorian year. The first ISO week can span the previous and current Gregorian years.
    W begins on the first Monday in a Gregorian year.
  • End of Year Weeks:
    U specifies that the last week (52 or 53) in the year can contain less than 7 days. A Sunday to Saturday period that spans 2 consecutive Gregorian years is designated as 52 and 0 or 53 and 0.
    V specifies that the last week (52 or 53) of the ISO year contains 7 days. However, the last week of the ISO year can span the current Gregorian and next Gregorian year.
    W specifies that the last week (52 or 53) in the year can contain less than 7 days. A Monday to Sunday period that spans two consecutive Gregorian years is designated as 52 and 0 or 53 and 0.

Example

The following example shows the values of the U, V, and W descriptors for dates near the end of certain years and the beginning of the next year. Examining the full data set illustrates how the behavior can differ between the various descriptors depending on the day of the week for January 1. The output displays the first 20 observations:
title 'Values of the U, V, and W Descriptors';
data a(drop=i date0 date1 y);
     date0 = '20dec2005'd;
     do y = 0 to 5;
        date1 = intnx("YEAR",date0,y,'s');
        do i = 0 to 20;
          date = intnx("DAY",date1,i);
          year = YEAR(date);
          week   = week(date); 
          week_u = week(date, 'u'); 
          week_v = week(date, 'v'); 
          week_w = week(date, 'w'); 
          output;
        end;
     end;
     format date WEEKDATX17.;
run;
proc print;
run;
Results of Identifying the Values of the U, V, and W Descriptors
Results of Identifying the Values of the U, V, and W Descriptors

See Also

Functions:
Formats:
WEEKUw. Format in SAS Formats and Informats: Reference
WEEKVw. Format in SAS Formats and Informats: Reference
WEEKWw. Format in SAS Formats and Informats: Reference
Informats:
WEEKUw. Informat in SAS Formats and Informats: Reference
WEEKVw. Informat in SAS Formats and Informats: Reference
WEEKWw. Informat in SAS Formats and Informats: Reference