Week Beginning and End

So you've been asked to compare the week on week changes in data, no problem!!......Except the data set you have only has the data per individual day.

If only there was a way to convert the individual dates to their corresponding weekdate! As you've probably guessed by now with SAS their is always a solution, in this case it's the INTNX function.

(INTNX('week.2', date_variable, 0, 'beginning'))

Creating a new column and setting it equal to the above function converts a date variable to a weekdate. Each weekdate begins on a Monday however this can easily be changed by changing the integer following 'week.2' E.g. Changing this to 'week.1' will bring back weekdates starting from Sunday.

The second argument in the function is where your date variable goes, however what is even more interesting is what the third and fourth argument allow you to do. If the third argument is changed from 0 to 1 instead, SAS will offset the weekdate by one week, e.g. if the start of the week is 25JUL2011, SAS will shift this to 01AUG2011 instead. This can be extremely useful at times.

The fourth argument specifies whether you want your weekdate to correspond to the beginning of the week or the end of the week. This can be achieved by changing 'beginning' to 'end'.

Problem Solved!