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.