space separated list intersection - sas

Question

Note: code edited after remarks from #user667489 but issues remain.
I built a fairly simple macro to return the intersection of 2 space separated lists as a new space separated list but for some reason the definition of the macro returns errors.
The macro loops through both lists and keep an element if a match is found (very straightforward, no handling of duplicates or optimization).
I cannot make sense of the log, which shows a combination of following error messages:
ERROR: Macro keyword LET appears as text.
ERROR: Macro keyword MACRO appears as text.
%macro list_intersection
(list1= /* space separated list, or unique term */
,list2= /* space separated list, or unique term */
);
%local output;
%local i;
%local j;
%let i = 1;
%let j = 1;
%do %while (%length(%scan(&list1,&i)));
%do %while (%length(%scan(&list2,&j)));
%if (%scan(&list1,&i) = %scan(&list2,&j)) %then
%let output = &output %scan(&list1,&i);
%let j = %eval(&j+1);
%end;
%let i = %eval(&i+1);
%end;
&output
%mend;
Can you help me circling the issue ?
I'm also open to a more efficient/robust/simple way of achieving the same output.
Reproducible log
Using SAS 9.3, I put above code in a separate program for it not to be polluted, save project, close and reopen. Open program, click run button, and here is the complete log:
1 The SAS System 09:50 Monday, January 22, 2018
1 ;*';*";*/;quit;run;
2 OPTIONS PAGENO=MIN;
3 %LET _CLIENTTASKLABEL='Program3';
ERROR: Macro keyword LET appears as text.
4 %LET _CLIENTPROJECTPATH='F:\CI\Projects\Wealth Indicators\106 Explore DIM_PHYSICALPERSON\SAS\Rework_table_auto2.egp';
ERROR: Macro keyword LET appears as text.
5 %LET _CLIENTPROJECTNAME='Rework_table_auto2.egp';
ERROR: Macro keyword LET appears as text.
6 %LET _SASPROGRAMFILE=;
ERROR: Macro keyword LET appears as text.
7
8 ODS _ALL_ CLOSE;
9 OPTIONS DEV=ACTIVEX;
10 GOPTIONS XPIXELS=0 YPIXELS=0;
11 FILENAME EGSR TEMP;
12 ODS tagsets.sasreport13(ID=EGSR) FILE=EGSR STYLE=HtmlBlue
12 ! STYLESHEET=(URL="file:///C:/Program%20Files/SASHome/x86/SASEnterpriseGuide/5.1/Styles/HtmlBlue.css") NOGTITLE NOGFOOTNOTE
12 ! GPATH=&sasworklocation ENCODING=UTF8 options(rolap="on");
13
14 GOPTIONS ACCESSIBLE;
15 %macro list_intersection
ERROR: Macro keyword MACRO appears as text.
16 (list1= /* space separated list, or unique term */
17 ,list2= /* space separated list, or unique term */
18 );
19 %local output;
ERROR: Macro keyword LOCAL appears as text.
20 %local i;
ERROR: Macro keyword LOCAL appears as text.
21 %local j;
ERROR: Macro keyword LOCAL appears as text.
22 %let i = 1;
ERROR: Macro keyword LET appears as text.
23 %let j = 1;
ERROR: Macro keyword LET appears as text.
24 %do %while (%length(%scan(&list1,&i)));
ERROR: Macro keyword DO appears as text.
25 %do %while (%length(%scan(&list2,&j)));
ERROR: Macro keyword DO appears as text.
26 %if (%scan(&list1,&i) = %scan(&list2,&j)) %then
ERROR: Macro keyword IF appears as text.
27 %let output = &output %scan(&list1,&i);
28 %let j = %eval(&j+1);
ERROR: Macro keyword LET appears as text.
29 %end;
ERROR: Macro keyword END appears as text.
30 %let i = %eval(&i+1);
ERROR: Macro keyword LET appears as text.
31 %end;
ERROR: Macro keyword END appears as text.
32 &output
33 %mend;
ERROR: Macro keyword MEND appears as text.
34
35 GOPTIONS NOACCESSIBLE;
36 %LET _CLIENTTASKLABEL=;
ERROR: Macro keyword LET appears as text.
37 %LET _CLIENTPROJECTPATH=;
2 The SAS System 09:50 Monday, January 22, 2018
ERROR: Macro keyword LET appears as text.
38 %LET _CLIENTPROJECTNAME=;
ERROR: Macro keyword LET appears as text.
39 %LET _SASPROGRAMFILE=;
ERROR: Macro keyword LET appears as text.
40
41 ;*';*";*/;quit;run;
42 ODS _ALL_ CLOSE;
43
44
45 QUIT; RUN;
46
Initial code before edit:
%macro list_intersection
(list1= /* space separated list, or unique term */
,list2= /* space separated list, or unique term */
);
%local output =;
%local i = 1;
%local j = 1;
%do %while (%length(%scan(&list1,&i)));
%do %while (%length(%scan(&list2,&j)));
%if (%scan(&list1,&i) = %scan(&list2,&j) %then
%local output = &output %scan(&list1,&i);
%let j = %eval(&j+1);
%end;
%let i = %eval(&i+1);
%end;
&output
%mend;

Answer 1

A few things immediately stand out:
You cannot use %local to set a value for a macro variable. Instead of %local i=1; you must write two separate statements: %local i; %let i = 1;. %local initialises macro variables to an empty string.
You have unbalanced brackets in your %if statement.
Try moving %let j = %eval(&j+1); into the outer %do %while loop.
Also, you probably want to make sure that %scan only uses space as a delimiter - it defaults to space plus . < ( + & ! $ * ) ; ^ - / , % |
Here's a working version:
%macro list_intersection
(list1= /* space separated list, or unique term */
,list2= /* space separated list, or unique term */
);
%local output;
%local i;
%local j;
%let i = 1;
%do %while (%length(%scan(&list1,&i,%str( ))));
%let j = 1;
%do %while (%length(%scan(&list2,&j,%str( ))));
%if %scan(&list1,&i,%str( )) = %scan(&list2,&j,%str( )) %then
%let output = &output %scan(&list1,&i,%str( ));
%let j = %eval(&j+1);
%end;
%let i = %eval(&i+1);
%end;
&output
%mend;
%put %list_intersection(list1=1 2 3,list2=2 3 4);

Answer 2

You can use SAS functions to make that much easier. Use the COUNTW() function to find the upper bound for the %DO loop. Use the FINDW() function to test if word is found in the other list.
%macro list_intersection
(list1 /* space separated list of terms */
,list2 /* space separated list of terms */
);
%local output i next ;
%do i=1 %to %sysfunc(countw(&list1,%str( ))) ;
%let next=%scan(&list1,&i,%str( ));
%if %sysfunc(findw(&list2,&next,,s)) %then %let output=&output &next ;
%end;
&output
%mend;
You could include the i modifier in the findw() call to make it case insensitive. You could also test if the word is already in the output string to eliminate duplicates.
%macro list_intersection_nodups
(list1 /* space separated list of terms */
,list2 /* space separated list of terms */
);
%local output i next ;
%do i=1 %to %sysfunc(countw(&list1,%str( ))) ;
%let next=%scan(&list1,&i,%str( ));
%if %sysfunc(findw(&list2,&next,,si)) and not %sysfunc(findw(&output,&next,,si))
%then %let output=&output &next ;
%end;
&output
%mend;
Example:
274 %put %list_intersection_nodups(A B a C,a c d);
A C