COMPRESS: SAS Function strips characters from the string

In SAS 9.1.3 , an extra argument (MODIFIER) is added to the SAS character string function COMPRESS and these modifiers modifies the action of the COMPRESS function;
Syntax: COMPRESS(<, chars><, modifiers>) ;

Following characters can be used as modifiers.

a – Compress or Delete all upper and lower case characters from String.

ak- Compress or Delete alphabetic characters(1,2,3 etc) from String.

kd- Compress or Delete characters(aplabets) from String.( Keeps only digits).

d – Compress or Delete numerical values from String.

i – Compress or Delete specified characters both upper and lower case from String.

k – keeps the specified characters in the string instead of removing them.

l – Compress or Delete lowercase characters from String.

p – Compress or Delete Punctuation characters from String.

s – Compress or delete spaces from String. This is default.

u – Compress or Delete uppercase characters from String.
See the Example below:

data _null_ ;

string='StudySAS Blog! 17752. ' ;
string1=compress(string,'') ; *Compress spaces. This is default;
string2=compress(string,'','ak');*Compress alphabetic chars(1,2etc);
string3=compress(string,'','d') ; *Compress numerical values;
string4=compress(string,'','l');*Compress  lowercase characters;
string5=compress(string,'','u');*Compress uppercase characters;
string6=compress(string,'S','k');*Keeps only specifiedcharacters;
string7=compress(string,'!.','P');*Compress Punctuations only;
string8=compress(string,'s','i');*upper/lower case specified characters;
string9=compress(string,'','a');*Compress all upper\lower case  characters ;
string10=compress(string,'','s') ; * Compress or delete spaces;
string11=compress(string,'','kd') ; *Compress alphabets (Keeps only digits);
put string1= ;
put string2= ;
put string3= ;
put string4= ;
put string5= ;
put string6= ;
put string7= ;
put string8= ;
put string9= ;
put string10=;
put string11=;
run ;

OUTPUT:

string1=StudySASBlog!17752.

string2=StudySAS Blog
string3=StudySASBlog!.
string4=SSASB!17752.
string5=tudylog!17752.
string6=SSS
string7=StudySAS Blog 17752
string8=tudyA Blog! 17752.
string9=!17752.
string10=StudySASBlog!17752.
string11=17752