topic Re: How to use character variables in if then statement in an array in SAS. in SAS Programming

How to use character variables in if then statement in an array in SAS.

CynthiaWei — Tue, 08 Oct 2019 08:22:22 GMT

Hi,

I am having an array of variables day1-day10 (10 variables) including character values there, such as a1, b32, c56, d9876, e298, and f402. I want to create a new variable---important_day. Only when day1 (or day2, day3, or...day10)=f402 then important_day=Yes, when day1 (or day2, day3, or...day10) is anyone else then important_day=No.

Please advice how to use character variables in if then statement in an array in SAS.

Thank you in advance!

with regards,

Re: How to use character variables in if then statement in an array in SAS.

PeterClemmensen — Tue, 08 Oct 2019 08:32:56 GMT

Like this?

data have;
input (day1-day10)(:$);
datalines;
a1 b32 c56 d9876 e298 f402 a1 b32 c56 d9876 e298
a1 b32 c56 d9876 e298 a1   a1 b32 c56 d9876 e298
;

data want;
    set have;
    array d{10} day1-day10;
    important_day=ifc(whichc('f402', of d[*]) > 0, 'Yes', 'No');
run;

Re: How to use character variables in if then statement in an array in SAS.

CynthiaWei — Tue, 08 Oct 2019 08:42:01 GMT

I tried, but it didn't work.
what does ifc mean?

Re: How to use character variables in if then statement in an array in SAS.

PeterClemmensen — Tue, 08 Oct 2019 08:45:47 GMT

What do you mean by 'it didn't work'? Did you get an error in the log or did the results just differ from what you want? And if so, how? 🙂

The IFC Function Simply returns 'Yes' if the first argument is true ('f402' is there) and 'No' if the first argument is false ('f402' is not there).

Re: How to use character variables in if then statement in an array in SAS.

PeterClemmensen — Tue, 08 Oct 2019 09:06:48 GMT

Just to be clear, the above is equivalent to

data want;
    set have;
    array d{10} day1-day10;
    if whichc('f402', of d[*]) > 0 then important_day='Yes';
    else                                important_day='No';
run;

Re: How to use character variables in if then statement in an array in SAS.

hashman — Tue, 08 Oct 2019 09:11:35 GMT

@PeterClemmensen:

There's no need for WHICHC, as the search can be done directly against the direct array name reference:

data have ;                                                                                                                                                                                                                                                     
  input (day1-day10) ($) ;                                                                                                                                                                                                                                      
  cards ;                                                                                                                                                                                                                                                       
a1 b32 c56 d9876 e298 f402 a1 b32 c56 d9876 e298                                                                                                                                                                                                                
a1 b32 c56 d9876 e298 a1   a1 b32 c56 d9876 e298                                                                                                                                                                                                                
;                                                                                                                                                                                                                                                               
run ;                                                                                                                                                                                                                                                           
                                                                                                                                                                                                                                                                
data want ;                                                                                                                                                                                                                                                     
  set have ;                                                                                                                                                                                                                                                    
  array d day: ;                                                                                                                                                                                                                                                
  important_day = put (ifc ("f402" in d, "yes", "no"), $3.) ;                                                                                                                                                                                                   
run ;

Kind regards

Paul D.

Re: How to use character variables in if then statement in an array in SAS.

ed_sas_member — Tue, 08 Oct 2019 09:13:20 GMT

You can try also this

data want;
    set have;
    length important_day $3;
    important_day="No";
    array day(10) $;
    do i=1 to dim(day);
    	if day(i)= "f402" then do;
    		important_day="Yes";	/* When "f402" is found, change the flag variable to "Yes" */
    		leave;	/* No need to continue checking because "f402" is found */
    	end;
    end;
run;

Re: How to use character variables in if then statement in an array in SAS.

PeterClemmensen — Tue, 08 Oct 2019 09:15:40 GMT

@hashman of course. Good catch!

Re: How to use character variables in if then statement in an array in SAS.

Tom — Tue, 08 Oct 2019 12:42:14 GMT

Not sure how using one method (IN operator) is better/worse than the other (WHICHC() function).

Note that if you use the function there is no need to define an array.

Re: How to use character variables in if then statement in an array in SAS.

hashman — Tue, 08 Oct 2019 19:34:18 GMT

@Tom:

I don't think it's a matter of "better" or "worse"; just two different pieces of SAS functionality.

If you only want to know if the value to which an expression resolves is present an array A, then coding:

<expression> IN A

is less busy code-wise (and, IMO, more self-explanatory) than:

whichn (<expression>, of A[*]) > 0

Besides, IN is good for both numeric and character arrays, while WHICHN/C has to be type-specific. If you want to know the index of the first array item where <expression> is found, then of course IN doesn't tell while WHICHN/C does.

Performance-wise:

Both use sequential search, so both execute in O(N) time.
IN doesn't use any extra memory over the memory allocated for the array, no matter how many times the compiler sees it.
WHICHN/C uses extra memory equal to that allocated for the array for every reference to WHICHN/C the compiler sees.

For example, run the following two pieces of code and compare their RAM footprints:

option fullstimer ;                                                                                                                     
data _null_ ;                                                                                                                           
  array a [1000000] _temporary_ (1:1000000) ;                                                                                           
  do x = 1, 500000, 1000000 ;                                                                                                           
    f1 = x     in a ;                                                                                                                   
    f2 = x + 1 in a ;                                                                                                                   
    f3 = x - 1 in a ;                                                                                                                   
    put (f1-f3) (=) ;                                                                                                                   
  end ;                                                                                                                                 
run ;                                                                                                                                   
data _null_ ;                                                                                                                           
  array a [1000000] _temporary_ (1:1000000) ;                                                                                           
  do x = 1, 500000, 1000000 ;                                                                                                           
    f1 = whichn (x,     of a[*]) > 0 ;                                                                                                  
    f2 = whichn (x + 1, of a[*]) > 0 ;                                                                                                  
    f3 = whichn (x - 1, of a[*]) > 0 ;                                                                                                  
    put (f1-f3) (=) ;                                                                                                                   
  end ;                                                                                                                                 
run ;

Then comment out one or two calls for IN and WHICHN and watch what FULLSTIMER reports compared to the uncommented version.

Kind regards

Paul D.

Re: How to use character variables in if then statement in an array in SAS.

CynthiaWei — Fri, 11 Oct 2019 23:23:33 GMT

I really appreciate your help!
Best regards,

Re: How to use character variables in if then statement in an array in SAS.

CynthiaWei — Fri, 11 Oct 2019 23:24:20 GMT

I really appreciate your help!
Best regards,

Re: How to use character variables in if then statement in an array in SAS.

CynthiaWei — Sat, 12 Oct 2019 03:26:09 GMT

Thank you very much!