topic Re: How do I determine length of variable in SAS Data Management

How do I determine length of variable

sri1 — Mon, 28 Oct 2019 11:44:26 GMT

Hi all,

I have the following sample code and want to create the variable "Name" with maximum length of strings in variable name instead of default $200 and I would like the length to be updated when the dataset changes.Is there anyway I can do in datastep?

data attrs;
dsid=open("sashelp.class", "i");
n_vars=attrn(dsid, "nvars");
do i=1 to n_vars;
Name=varname(dsid, i);
Type=vartype(dsid, i);

output;

end;

rc=close(dsid);

run;

Your solutions are highly appreciated.

Thanks

Re: How do I determine length of variable

rudfaden — Mon, 28 Oct 2019 12:18:17 GMT

Not that elegant. But it works.

Save the max length of name in a macro.

data attrs;
dsid=open("sashelp.class", "i"); 
n_vars=attrn(dsid, "nvars");
do i=1 to n_vars;
Name=varname(dsid, i);
Type=vartype(dsid, i);

output;
call symput('len',max(length(name)));

end;
rc=close(dsid);
run;

Alter the length of the column.

proc sql;
alter table attrs
  modify Name char(&len);
quit;

Re: How do I determine length of variable

mkeintz — Mon, 28 Oct 2019 12:29:33 GMT

I would assign a fixed length of $32 to the variable name, since that is the maximum allowable length of any sas variable name.

See Rules for most SAS names

Re: How do I determine length of variable

Tom — Mon, 28 Oct 2019 12:33:19 GMT

Why does it matter what length the variable has, as long as the length is not too SHORT?

proc sql noprint;
  select max(length(NAME)) into :max_length trimmed
  from sashelp.class
  ;
quit;

data class ;
  length name $&max_length. ;
  set sashelp.class;
run;

Re: How do I determine length of variable

rudfaden — Mon, 28 Oct 2019 12:34:53 GMT

If a variable is to long it will use unessesary space and SAS will run slower. Not a big deal if you have small dataset. But if you have billions of rows it matters.

Re: How do I determine length of variable

mkeintz — Mon, 28 Oct 2019 12:42:44 GMT

Question: Are you trying the determine the longest length of all the varnames (that is my assumption)? Or are you trying to determine the longest value of a variable called NAME?

Re: How do I determine length of variable

sri1 — Mon, 28 Oct 2019 13:06:52 GMT

@mkeintz You are right.I am trying to determine the longest length of all the varnames

Re: How do I determine length of variable

sri1 — Mon, 28 Oct 2019 13:09:57 GMT

@TomThanks for your reply.I am trying to determine the maximum length of all the varnames but not NAME column of sashelp.class

Re: How do I determine length of variable

Tom — Mon, 28 Oct 2019 13:14:22 GMT

@sri1 wrote:

@TomThanks for your reply.I am trying to determine the maximum length of all the varnames but not NAME column of sashelp.class

Huh? Why? What are you going the change once you know that information?

The maximum length of a SAS variable name is 32 bytes.

Anyway the method to find the max is the same, only use as input the DICTIONARY metadata tables instead of the actual data.

Re: How do I determine length of variable

sri1 — Mon, 28 Oct 2019 15:33:03 GMT

@Tom I know that maximum length of a SAS variable name is 32 bytes but to reduce the storage space.

Re: How do I determine length of variable

mkeintz — Mon, 28 Oct 2019 13:28:37 GMT

@sri1

I can see the benefit of reducing the length of a variable from $200 to $32, just as a matter of good housekeeping, if nothing else. And if you were to load your resulting data set into memory (via the SASFILE statement or via a hash object) you could save a meaningful amount of memory for a large collection.

But I don't see nearly as much value in trying to cut down from $32, to (say) $15 based on the varnames actually in use. Using $32 guarantees you always will have allocated enough space, and also means you don't have to inspect all the metadata in order to establish the absolute minimum necessary length.

Re: How do I determine length of variable

TomKari — Mon, 28 Oct 2019 14:03:06 GMT

Consider using compression. I had a similar situation where I couldn't predict character variable length, and some outliers were VERY long, and when I used the compression option it reduced the overhead to a very manageable amount.

Tom