topic Re: Use of colon after a comparison operator in SAS Programming

Use of colon after a comparison operator

Oligolas — Fri, 05 Apr 2024 11:05:32 GMT

Hi,

can you guys explain why the colon seems not to trim the dates before comparing and why I get more errors than warnings here?

data test;
input rfxstdtc $ 1-10 impdtc $ 12-21 usubjid $ 23-30;
cards;
2023-10-12 2023-11-12 DEU-001F
2023-10    2023-10-13 DEU-001F
2023       2023-10-14 DEU-001F
2023-11    2023-10-13 DEU-001F
run;
data test1;
   set test;
   if rfxstdtc^='' and impdtc^='' and rfxstdtc ^=: impdtc then put 'E' 'RROR:# Imputation occurred on different partials dates ' _N_= USUBJID= rfxstdtc= impdtc= ; 
   if rfxstdtc^='' and impdtc^='' and strip(rfxstdtc) ^=: strip(impdtc) then put 'W' 'ARNING:# Imputation occurred on different partials dates ' _N_= USUBJID= rfxstdtc= impdtc= ; 
run;

Re: Use of colon after a comparison operator

PaigeMiller — Fri, 05 Apr 2024 11:55:33 GMT

Explain, please. What is wrong with the results in the log? What is the expected result?

Re: Use of colon after a comparison operator

FreelanceReinh — Fri, 05 Apr 2024 12:11:52 GMT

Hi @Oligolas,

The comparison is restricted to the length of the shorter string, including trailing blanks, if any.

Example:

436   data _null_;
437   if 'AB' =:'ABC'  then put 'true1';
438   if 'AB '=:'ABC'  then put 'false';
439   if 'AB '=:'AB C' then put 'true2';
440   run;

true1
true2

The first comparison looks at two characters, the second and third comparison include three.

Your rfxstdtc and impdtc values contain ten characters since 10 is the defined length of both variables, so the comparisons without STRIP (or TRIM) are based on all ten characters. The expressions returned by the STRIP function are shorter if (leading or) trailing blanks were present in the arguments, so the comparisons change correspondingly.

Re: Use of colon after a comparison operator

Tom — Fri, 05 Apr 2024 15:54:56 GMT

Why would you use STRIP() instead of TRIM()?

Do you expect the values to have leading spaces? And if so why do you want to remove the leading spaces?

Re: Use of colon after a comparison operator

Oligolas — Wed, 10 Apr 2024 09:07:20 GMT

Hi @Tom I do not 'expect' it, I only use strip as a standard to compare strings

Re: Use of colon after a comparison operator

Oligolas — Wed, 10 Apr 2024 09:13:07 GMT

@PaigeMiller I obviously took a statement in a paper 'as is' without checking it's validity or I simply misunderstood it

"These operators compare two strings after making the strings the same length by truncating the longer string to the same length as the shorter string."