Another way(and simpler) to solve practice question m104p11 on page 224 ,Macro1: Essentials pdf

[dxiao2017]

I cannot access github btw

[Quentin · Accepted solution]

That shown style of looping over a list with %DO %UNTIL was common prior to the introduction of the COUNTW function.  I think COUNTW was introduced in v7 or v8. 

I would agree that using COUNTW to count the number of items in a list seems clearer to me also.

[quickbluefish]

Agree with others here - I would just add that with COUNTW and SCAN (and similar), it's a good idea to specify your delimiter as the optional last argument - otherwise, SAS will try to guess.  And further, if the delimiter is a space (as it is here), never a bad idea to clean up potential multiple whitespace characters with %CMPRES:

%let YRLIST=2012 2014 2016;
%let YRLIST=%CMPRES(&YRLIST);
%let nYRS=%sysfunc(countW(&YRLIST,' '));

.... %let YR=%SCAN(&YRLIST, &i, ' ');

* you can also use %STR( ) instead of ' ' above ;

[dxiao2017]

Thanks a lot for your comments! I tested your examples and somehow got something like this (see below). I have three questions: 1) it looks like the %cmpres function is not necessary (at least in my example), if I run the %cmpres statement I got error message; 2) if I want to clean up whitespace characters the function to be use is compbl (I do not know how this function is written when it is a macro function), not compress, am I right or wrong? 3) this question is not relevant, how can I make the code posted here colored?

(after I post THIS message I found it is colored somehow, however, the code in my previous post were not)

%let yrlist=%nrstr(2010 % 2012 2014,2016   2018 & 2019);
*%let yrlist=%cmpres(&yrlist,'%,&');
*%put &yrlist;
%let nyrs=%sysfunc(countw(&yrlist,' %,&'));
%put &nyrs;

[Quentin]

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@quickbluefish wrote:

Agree with others here - I would just add that with COUNTW and SCAN (and similar), it's a good idea to specify your delimiter as the optional last argument - otherwise, SAS will try to guess.  And further, if the delimiter is a space (as it is here), never a bad idea to clean up potential multiple whitespace characters with %CMPRES:

%let YRLIST=2012 2014 2016;
%let YRLIST=%CMPRES(&YRLIST);
%let nYRS=%sysfunc(countW(&YRLIST,' '));

.... %let YR=%SCAN(&YRLIST, &i, ' ');

* you can also use %STR( ) instead of ' ' above ;

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I agree it's good practice to specify the delimiter for COUNTW and %SCAN.  Particularly because if you have an empty list, %sysfunc(countw()) will throw an error, but %sysfunc(countw(,%str( )))  will return 0.

That said, I think it's much clearer/better to use %STR( ) to specify the blank as delimiter, rather than ' '.  If you use ' ' you're telling the macro processor to use both blank and a single quote as delimiters.  In the macro language ' ' is a three character string, not a single blank.

[dxiao2017]

PS: the countw() function and the code I took as reference is on page37, page41 of SAS Programming3: Advanced Techniques course notes PDF.