Scripting Guide - SAS

Chapter 8 Programming Methods 185
Lists and Expressions
Note, however, that in column formulas, eval only works if it is outermost in the formula. So, for example,
Formula(log(eval(column name(i))))
would generate an error. Instead, use
Formula(Eval(Substitute(expr(log(xxx)),expr(xxx), column name(i))))
As another example,
Formula(eval(column name(i))+10)
generates an error, since eval is actually under the Add function. Instead, use
Formula(Eval(Substitute(expr(xxx+10), expr(xxx), column name(i))))
Retrieve a stored expression, not its result
What if you wanted the symbolic value of a global (such as the expression
Distribution(Column(height)) stored in dist above), rather than the evaluation of it (the actual
launched platform)? The Name Expr function does this. Name Expr retrieves its argument as an expression
without evaluating it, but if the argument is a name, it looks up the name’s expression and uses that,
unevaluated.
Expr returns its argument exactly, whereas Name Expr looks up the expression stored in its argument. Name
Expr “unpacks” just one layer to get the expression, but does not keep unpacking to get the result.
For example, you would need to use this if you had an expression stored in a name and you wanted to edit
the expression:
popVar = Expr( Summation( i = 1, N Row(), (y[i] - Col Mean( y )) ^ 2 / N Row()
) );
Summation( i = 1, N Row(), (y[i] - Col Mean( y )) ^ 2 / N Row() )
unbiasedPopVar = substitute( name expr( popVar ), expr( wild()/nrow() ), expr(
(y[i] - Col Mean( y )) ^ 2 / ( N Row() - 1 ) ) );
Summation( i = 1, N Row(), (y[i] - Col Mean( y )) ^ 2 / (N Row() - 1) )
Compare x, Expr(x), NameExpr(x), and Eval(x) after submitting this script:
a=1; b=2; c=3;
x = Expr(a+b+c);
Table 8.1 Compare Eval, Name Expr, and Expr
Command and result
x;
6
Eval(x);
6
Explanation
Evaluates x to the expression a+b+c, and then evaluates the expression,
returning the result, 6 (unpacks all layers).
Equivalent to simply calling x.
Evaluates x to the expression a+b+c, and then evaluates the expression,
returning the result, 6 (unpacks all layers).