sas MACRO ampersand -

- 

%let test = one; %let 1 = two;  %put &test; %put &&test; %put &&&test; %put &&&&test; %put &&&&&test;

well. i'm totally beaten these ampersands. don't understand why need many ampersands before macro variable. there trick master usage of ampersand? btw, 5 results, correspondingly?

with single set of ampersands, pretty boring; after one, odd number of ampersands leads resolving twice, number of ampersands resolves once. use 1 ampersand resolve once , 3 ampersands resolve twice, unless have stock in company owns rights ampersand.

more interesting following test, shows why numbers of ampersands have value:

%let test = one; %let testtwo = one; %let 1 = two; %let two=three;  %put &test&one; %put &&test&one; %put &&&test&one; %put &&&&test&one; %put &&&&&test&one; %put &&&&&&test&one;

basically, each pass through, sas following:

  • resolve single ampersand plus text macro variable reference.
  • resolve pairs of ampersands 1 ampersand.

those done simultaneously , iteratively until ampersands gone, , each result kept next iteration , not affect current iteration. so, &test&one becomes onetwo because &test-> 1 , &one -> two. steps remaining:

  • &&test&one -> &testtwo -> one. &&|test|&one. double && before test becomes &, test remains, , &one resolves two. leaves &testtwo second pass resolves one.
  • &&&test&one -> &onetwo -> not resolve. &&|&test|&one -> &|one|two -> dnr.
  • &&&&test&one -> &&testtwo -> &testtwo -> one. &&|&&|test|&one -> &&|testtwo -> &testtwo -> one. 2 pairs each resolve down one, making 1 pair, resolves one, leaves &testtwo resolve.
  • &&&&&test&one similar 3 ampersand case, 1 pair.
  • &&&&&&test&one resolves &&&testtwo resolves &one resolves two. &&|&&|&&|test|&one -> &&|&testtwo -> &one -> two. odd number of pairs means 1 more set of resolves.

at end of day, need remember:

  • 1 ampersand resolves macro variable once , that's it.
  • 2 ampersands useful composite macro variables, ie, prefix plus macro-driven suffix (&&prefix&suffix).
  • 3 ampersands useful going 2 deep in resolving single macro variable (&&&var -> &var2 -> var3).
  • 6 ampersands useful resolving two-deep composite macro variable (ie, combining 2 , 3) ([&prefix=var, &suffix=2] &&&&&&prefix&suffix -> &&&var2 -> &var3 -> 4).

beyond that, 4 or more (other 6) useful particularly complex combinations; levels used delay resolution until particular times.


Comments

Post a Comment

Popular posts from this blog

c# - Unity IoC Lifetime per HttpRequest for UserStore -

-
i'm trying clean default implementation of accountcontroller.cs comes out of box in new mvc5/owin security implementation. have modified constructor this: private usermanager<applicationuser> usermanager; public accountcontroller(usermanager<applicationuser> usermanager) { this.usermanager = usermanager; } also, have created lifetime manager unity looks this: public class httpcontextlifetimemanager<t> : lifetimemanager, idisposable { private httpcontextbase _context = null; public httpcontextlifetimemanager() { _context = new httpcontextwrapper(httpcontext.current); } public httpcontextlifetimemanager(httpcontextbase context) { if (context == null) throw new argumentnullexception("context"); _context = context; } public void dispose() { this.removevalue(); } public override object get...
Read more

Change the color of an oval at click in Java AWT -

-
i have draw ovals in java, , @ click change color. beginning tried change color after 20 ms, doesn't work. my code is: public class mycomponentnew extends frame { public graphics2d g2d; public mycomponentnew(string title) { super(title); setsize(400, 550); } @override public void paint(graphics g) { this.g2d = (graphics2d) g; this.g2d.setcolor(color.red); this.g2d.filloval(10, 55, 50, 100); } public void changecolor () { this.g2d.setcolor(color.blue); this.g2d.filloval(10, 55, 50, 100); } } and in class main method have: mycomponentnew m; m = new mycomponentnew("fereastra cu baloane"); m.setvisible(true); m.addwindowlistener(new windowadapter() { @override public void windowclosing(windowevent we) { system.exit(0); } }); try { thread.sleep(20); } catch(interruptedexception e) {} m.changecolor(); the color of oval remains red. ...
Read more

I am trying to solve the error message 'incompatible ranks 0 and 1 in assignment' in a fortran 95 program. -

-
i writing program in fortran find velocity of parachuting person in relation time. keep getting error can't fix. new programming , appreciated. the error is v(i+1)=v(i)+[32-((c*v(i)*v(i))/m)]*(h) 1 error: incompatible ranks 0 , 1 in assignment @ (1) and program is program para integer :: real :: v(11) !velocity real :: q !initial velocity real :: h !time step real :: c !drag coefficient real :: m !mass ! gravity equal 32 ft/s^2 write (*,*)'enter time step' read(*,*)h write(*,*)'enter initial velocity' read(*,*)q write(*,*)'enter drag coefficient' read(*,*)c write(*,*)'enter mass' read(*,*)m i=1,10 ! 1 10, 1 being interval. end v(i+1)=v(i)+[32-((c*v(i)*v(i))/m)]*(h) q=v(1) end program you cannot use [] normal parenthesis in expressions. array constructor, [ items ] means array items elements. end do should after line.
Read more