| Control {base} | R Documentation |
These are the basic control-flow constructs of the R language. They function in much the same way as control statements in any algol-like language.
if(cond) expr if(cond) cons.expr else alt.expr for(var in seq) expr while(cond) expr repeat expr break next
Note that expr and cons.expr, etc, in the Usage section
above means an expression in a formal sense. This is either a
simple expression or a so called compound expression, usually
of the form { expr1 ; expr2 }.
Note that it is a common mistake to forget putting braces ({ .. })
around your statements, e.g., after if(..) or for(....).
In particular, you should not have a newline between } and
else to avoid a syntax error in entering a if ... else
construct at the keyboard or via source.
For that reason, one (somewhat extreme) attitude of defensive programming
uses braces always, e.g., for if clauses.
The index seq in a for loop is evaluated at the start of
the loop; changing it subsequently does not affect the loop.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Syntax for the basic R syntax and operators,
Paren for parentheses and braces; further,
ifelse, switch.
for(i in 1:5) print(1:i)
for(n in c(2,5,10,20,50)) {
x <- rnorm(n)
cat(n,":", sum(x^2),"\n")
}