How does SUBSTR= work with leading blanks

[mftuchman]

What would you expect the output of this code to be?  What about the value of x in the 'v2' put statement?

data _null_;
length x $200;
x='?';
substr(x,70,1)='!';
put 'v1' x= $char200.;
x=' ';
substr(x,60,8)='la chose';
put 'v2' x= $char200.;
run;

For the second one, I expected 59 blanks followed by the text.  This expectation was apparently in error.  How could I have predicted the observed behavior (X='la chose' with no leading blanks)?

Please don't ask me what I'm trying to do.  I already solved that; now I'm just curious as to how SUBSTR= works with blanks.  The SUBSTR (left side of 😃 page of the SAS documentation did not specify this behavior.

[data_null__ · Accepted solution]

---

@mftuchman wrote:

What would you expect the output of this code to be?  What about the value of x in the 'v2' put statement?

data _null_;
length x $200;
x='?';
substr(x,70,1)='!';
put 'v1' x= $char200.;
x=' ';
substr(x,60,8)='la chose';
put 'v2' x= $char200.;
run;

For the second one, I expected 59 blanks followed by the text.  This expectation was apparently in error.  How could I have predicted the observed behavior (X='la chose' with no leading blanks)?

Please don't ask me what I'm trying to do.  I already solved that; now I'm just curious as to how SUBSTR= works with blanks.  The SUBSTR (left side of 😃 page of the SAS documentation did not specify this behavior.

---

X= in the PUT statement specifies NAMED-PUT leading/trailing blanks are trimmed.

data _null_;
   length x $200;
   x='?';
   substr(x,70,1)='!';
   put 'v1' x $char200.;
   x=' ';
   substr(x,60,8)='la chose';
   put 'v2' x $char200.;
   run;

[mftuchman]

[to be deleted]

[ballardw]

Consider

data junk;
length x $200;
x='?';
substr(x,70,1)='!';
put 'v1' x= $char200.;
x=' ';
substr(x,60,8)='la chose';
l = length(x);

run;

If you open the data set junk with any of the SAS viewers you will see a bunch of leading spaces. The value of L will count the leading spaces plus the actual text ending at the 'e' in 'chose'.

[Tom]

Given that you seem to know what you are doing I am not sure I follow what the question is.

SAS stores all character variables as fixed lengths strings that are padded with spaces.  So if you start with a missing/null/empty variable of length 200 it has 200 spaces in it.  If you then change 70th position into an X it now has 69 spaces one X and then 130 spaces.

[mftuchman]

The question was originally "why do my leading spaces disappear?".   Is it possible that SUBSTR= does not do what I think it does?  But it does; it was the named PUT that threw me off.  When I surrounded it with delimiters, the spaces were visible.

And I have to remember that single quote works for SAS, but not for English grammar 🙂

[Astounding]

SUBSTR= does not replace X. Instead, it replaces some of the characters in X (in this case, characters 60 through 67), leaving any other characters in X unchanged.

[mftuchman]

Not trying to replace X - just trying to visualize a sparse vector in plain text, so I want to build a long blank string and then populate segments of it using substr=.

Turns out I got an easier to read result by using a non-destructive function CATX(OF ....) to build my string.

Hope that background helps a litt.e