Scripting Guide - SAS

Chapter 8 Programming Methods 195
Lists and Expressions
Substituting
show(polynomial);
polynomial = d * x ^ 3 + a * x ^ 2 + b * x + c
For the not-in-place operators, you must either state the expression directly or else quote a name that
evaluates to an expression using NameExpr. Such operators do not have From or Into in their names. They
return manipulated lists or expressions without changing the original list or expression given in the first
argument.
cubic=insert(expr(a*x^2 + b*x + c),expr(d*x^3),1);
d * x ^ 3 + a * x ^ 2 + b * x + c
quadratic=expr(a*x^2 + b*x + c);
cubic=insert(nameexpr(quadratic),expr(d*x^3),1);
d * x ^ 3 + a * x ^ 2 + b * x + c
Substituting is extremely powerful; please review the earlier discussion “Substituting,” p. 194. Here are a few
notes regarding substituting for expressions.
Substitute(pattern,name,replacement) substitutes for names in expressions
NameExpr looks through the name but copies instead of evaluates:
a = expr(distribution(column(x), normal quantile plot)); show(NameExpr(a));
NameExpr(a) = Distribution(Column(x), normal quantile plot)
Substitute evaluates all its arguments, so they must be quoted correctly:
b = substitute(NameExpr(a),expr(x),expr(weight)); show(NameExpr(b));
NameExpr(b) = Distribution(Column(weight), normal quantile plot)
SubstituteInto needs an L-value, so the first argument is not quoted:
SubstituteInto(a,expr(x),expr(weight)); show(NameExpr(a));
NameExpr(a) = Distribution(Column(weight), normal quantile plot)
Substitute is useful for changing parts of expressions, such as in the following example that tests the Is
functions:
data = {1, {1,2,3}, [1 2 3], "abc", x, x(y)};
ops = {is number, is list, is matrix, is string, is name, is expr};
m=J(n items(data),n items(ops),0);
test = expr(m[r,c] = _op(data[r]));
for (r=1,r