topic Re: check if a character is an alphabet in SAS Programming

check if a character is an alphabet

kurofufu — Wed, 08 Aug 2012 17:29:22 GMT

Suppose I have one character variable with length = 1 and I want to check if the value is an alphabet only.

Below is my code.Let me know if you have handier code.

data t2;

set t1;

if var1 in ("A","B","C","D", "E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y", "Z") then ind = 1;

else ind = 0;

run;

Re: check if a character is an alphabet

art297 — Wed, 08 Aug 2012 17:41:36 GMT

Do you only want to check for uppercase characters? Otherwise you could use:

data t2;

set t1;

ind=anyalpha(var1);

run;

if you really are only interested in upper case characters, you could use:

data t2;

set t1;

ind=anyupper(var1);

run;

Re: check if a character is an alphabet

Linlin — Wed, 08 Aug 2012 17:42:07 GMT

data t1;
input var1 $;
cards;
a
b
2
5
t
r
;
data t2;

set t1;

ind=ifn(lengthn(compress(var1,,'ka'))=1,1,0);

run;
proc print;run;

Re: check if a character is an alphabet

GeoffreyBrent — Thu, 09 Aug 2012 00:55:37 GMT

Another option is using regular expressions:

data t2;

set t1;

one_alpha_rx=prxparse("/[a-zA-Z]/");

ind=prxmatch(one_alpha_rx,x);

drop one_alpha_rx;

run;

For the problem you describe, you'd be better off using Art and Linlin's solutions - they're simpler and probably faster. But if you have to check more complex patterns some time, it's worth learning about regexp matching (this webform won't let me copy and paste, but there's a good paper on this in the SUGI29 archives).

As an example of where regexp comes in handy, I had an application where ID variables were expected to be twelve digits followed by an alpha character and then four more digits. To check whether inputs fit this rule, I used:

legal_pattern=prxparse("/\d{12}[a-zA-Z]\d{4}/");

Note that regexp matching doesn't check whether the variable EXACTLY matches the pattern defined, only whether it appears somewhere in there. But this isn't a problem if the length of the regexp exactly matches the length of the variable.

Re: check if a character is an alphabet

Amir — Thu, 09 Aug 2012 12:24:25 GMT

Hi,

A similar question was asked about specifying an alphabetic range:

https://communities.sas.com/thread/35517

HTH

Regards,

Amir.

Re: check if a character is an alphabet

TobyDunn_hotmail_com — Thu, 09 Aug 2012 13:28:01 GMT

kurofufu,

Ind = AnyAlpha( Var1 ) ;

Ind = PrxMatch( '/a-z/o' , Var1 ) ;

Either will do exactly what you want...... AnyAlpha will be slightly faster but isn't as portable given one has to know the translation table used for a specific set up...

Re: check if a character is an alphabet

GeoffreyBrent — Fri, 10 Aug 2012 01:50:08 GMT

Toby, have you tested that PrxMatch code? When I use that one I'm getting zeroes where they shouldn't be.

Re: check if a character is an alphabet

TobyDunn_hotmail_com — Fri, 10 Aug 2012 14:51:43 GMT

Geoffry,

Opps... I guess I shouldnt try to do too many things at the same time...the pattern modifier should have been a 'i' instead of 'o'.

It should have been:

Ind = PrxMatch( '/a-z/i' , Var1 ) ;

This will match a-z and A-Z characters as the 'i' pattern modifier tells the RegEx engine to use case insensitivity. There is no need for the 'o' pattern modifier since the pattern is explicitly and does not change. Which means SAS by default will only compile it once. Since Var1 is suppose to only be length of 1 the varibale does not need to be trimmed of any leading or trailing spaces.

If one only wanted to check for lower case letters then:

Ind = PrxMatch( '/a-z/' , Var1 ) ;

And for only upper case:

Ind = PrxMatch( '/A-Z/' , Var1 ) ;

Sorry for the fat fingered and lack of proofing on the last post.