SAS IML use of Mattrib with Macro (symget) in a loop - macros

Question

In an IML proc I have several martices and several vectors with the names of columns:
proc IML;
mydata1 = {1 2 3, 2 3 4};
mydata2 = {1 2, 2 3};
names1 = {'red' 'green' 'blue'};
names2 = {'black' 'white'};
To assign column names to columns in matrices one can copypaste the mattrib statement enough times:
/* mattrib mydata1 colname=names1;*/
/* mattrib mydata2 colname=names2;*/
However, in my case the number of matrices is defined at execution, thus a do loop is needed. The following code
varNumb=2;
do idx=1 to varNumb;
call symputx ('mydataX', cat('mydata',idx));
call symputx ('namesX', cat('names',idx));
mattrib (symget('mydataX')) colname=(symget('namesX'));
end;
print (mydata1[,'red']) (mydata2[,'white']);
quit;
however produces the "Expecting a name" error on the first symget.
Similar question Loop over names in SAS-IML? offers the macro workaround with symget, what produces an error here.
What is the correct way of using mattrib with symget? Is there other way of making a variable from a string than macro?
Any help would be appreciated.
Thanks,
Alex
EDIT1
The problem is in the symget function. The &-sign resolves the name of the matrix contained in the macro variable, the symget only returns the name of the macro.
proc IML;
mydata1 = {1 2 3};
call symputx ('mydataX', 'mydata1');
mydataNew = (symget('mydataX'));
print (&mydataX);
print (symget("mydataX"));
print mydataNew;
quit;
results in
mydata1 :
1 2 3
mydata1
mydataNew :
mydata1
Any ideas?
EDIT2
Function value solves the symget problem in EDIT1
mydataNew = value(symget('mydataX'));
print (&mydataX);
print (value(symget("mydataX")));
print mydataNew;
The mattrib issue but persists.
SOLVED
Thanks Rick, you have opened my eyes to CALL EXECUTE() statement.

Answer 1

When you use CALL SYMPUTX, you should not use quotes for the second argument. Your statement
call symputx ('mydataX', 'mydata1');
assigns the string 'mydata1' to the macro variable.
In general, trying to use macro variables in SAS/IML loops often results in complicated code. See the article Macros and loops in the SAS/IML language for an indication of the issues caused by trying to combine a macro preprocessor with an interactive language. Because the MATTRIB statement expects a literal value for the matrix name, I recomend that you use CALL EXECUTE rather than macro substitution to execute the MATTRIB statement.
You are also having problems because a macro variable is always a scalar string, whereas the column name is a vector of strings. Use the ROWCAT function to concatenate the vector of names into a single string.
The following statements accomplish your objective without using macro variables:
/* Use CALL EXECUTE to set matrix attributes dynamically.
Requires that matrixName and varNames be defined at main scope */
start SetMattrib;
cmd = "mattrib " + matrixName + " colname={" + varNames + "};";
*print cmd; /* for debugging */
call execute(cmd);
finish;
varNumb=2;
do idx=1 to varNumb;
matrixName = cat('mydata',idx);
varNames = rowcat( value(cat('names',idx)) + " " );
run SetMattrib;
end;