Scripting Guide - SAS

194 Programming Methods Chapter 8
Lists and Expressions
Substituting
Substitute and Substitute Into merit further discussion. Both find all matches to a pattern in a list
(or expression) and replace them with another expression. Each pattern must be a name. The arguments are
evaluated before they are applied, so most of the time you must quote them with an Expr function.
Substitute({a,b,c}, expr(a), 23); // produces {23,b,c}
Substitute(expr(sine(x)),expr(x),expr(y)); // produces sine(y)
To delay evaluating an argument, use NameExpr instead of Expr:
a={quick,brown,fox,jumped,over,lazy,dogs};
b=Substitute(a,expr(dogs),expr(cat));
canine=expr(dogs);equine=expr(horse);
c=Substitute(a,nameexpr(canine),nameexpr(equine)); show(a,b,c);
a = {quick,brown,fox,jumped,over,lazy,dogs}
b = {quick,brown,fox,jumped,over,lazy,cat}
c = {quick,brown,fox,jumped,over,lazy,horse}
Substitute Into does the same work, in place:
Substitute Into(a,expr(dogs),expr(horse));
You can list multiple pattern and replacement arguments to do more than one replacement in a single step:
d=Substitute(a,
nameexpr(quick),nameexpr(fast),
nameexpr(brown),nameexpr(black),
nameexpr(fox),nameexpr(wolf)
);
{fast,black,wolf,jumped,over,lazy,dogs}
Note that substitutions are done repeatedly over multiple instances of the expression pattern. For example:
Substitute(expr(a+a), expr(a), expr(aaa));
results in:
aaa + aaa
Manipulating expressions
The operators for manipulating lists can also operate on most expressions. Be sure to quote the expression
with Expr. For example:
Remove(Expr(A+B+C+D),2); // results in the expression A+C+D
b=Substitute(expr(log(2)^2/2), 2, 3); // results in the expression Log(3)^3/3
As with lists, remember that the first argument for in-place operators must be an L-value. An L-value is an
entity such as a global variable whose value can be set. In-place operators are those that operate on lists or
expressions directly. They have From or Into in their names (for example, Remove From and Insert
Into). They do not return a result; you have to show the expression to see the result.
polynomial=expr(a*x^2 + b*x + c);
insertinto(polynomial,expr(d*x^3),1);