INTCK Function Problem

[PeterClemmensen]

Hi All.

Can you perhaps offer some knowledge here? Why does this

data _null_;
   start='01feb2016'd;
   end='29feb2016'd;
   numMondays=intck('weekday134567w' ,start, end);
   put numMondays;
run;

not result in numMondays=5?

Browsing the INTCK Documentation and Intervals Available to the Function, I would think that this gives me the number of 1 day week periods, considering Tuesday, Wednesday, Thursday, Friday, Saturday ans Sunday as weekend days = the number of Mondays. However, clearly this is not the case as NumMondays=4 in the code above and there are 5 Mondays in February of 2016. 

[Astounding · Accepted solution]

First thing to check: INTCK captures the number of boundaries crossed. So if Feb 1 is a Monday it won't be counted.

[PeterClemmensen]

There we go. Thank you! Starring myself blind on this one.

[Kurt_Bremser]

Just to help with illustrating @Astounding 's point, run this for testing:

data _null_;
   start='01feb2016'd;
   end='29feb2016'd;
   numMondays=intck('weekday134567w' ,start, end);
   put numMondays;
run;

data _null_;
   start='31jan2016'd;
   end='29feb2016'd;
   numMondays=intck('weekday134567w' ,start, end);
   put numMondays;
run;

data _null_;
   start='01feb2016'd;
   end='01mar2016'd;
   numMondays=intck('weekday134567w' ,start, end);
   put numMondays;
run;

Only the second step returns 5, as the start is now before a Monday. Moving the end to a Tuesday does not change the result, so the boundary has to be 00:00 on a given day. 29feb is already past that boundary, but 01feb is not before it.

[PeterClemmensen]

Cool stuff. Thank you both 🙂