Conditional Expressions and Operators
DESCRIPTION:
Conditionally evaluates expressions. Either an if expression or an if-else expression is possible.
USAGE: 
if(test) true.expr
if(test) true.expr else false.expr


e1 || e2
e1 && e2
REQUIRED ARGUMENTS:
test,:
logical expression of length 1.
e1,:
logical expression of length 1.
e2,:
logical expression of length 1.
VALUE:
The if construct in the language evaluates test. If it is TRUE (i.e., if the first element of the result coerced to mode logical is TRUE), then true.expr is evaluated and returned as the value of the whole expression. Otherwise, the value of the expression is false.expr if present, or an empty value otherwise.

&& returns TRUE if both of its operands are TRUE (in the same sense as test above). If the left operand is not TRUE, the right operand is not evaluated.

|| returns TRUE if one of its operands is TRUE (in the same sense as test above). If the left operand is TRUE, the right operand is not evaluated.

DETAILS:
An NA value for the test causes an error.

The && and || operators are members of the Ops group of generic functions.

SEE ALSO:
Logic for element-wise logical operations ( | , & , ! and xor ); ifelse for parallel selection of values; and switch for multi-branch selections.
EXAMPLES: 
if(mode(x)!="character" && min(x)>0) log(x)
  # log(x) is an error if mode(x) is "character"


if (is.na(okay)) z <- z+1 else if (okay) {y <- rnorm(1); x <- runif(1)}