Expressions
R provides different constructs for grouping together expressions: semicolons, parentheses, and curly braces.
Separating Expressions
You can write a series of expressions on separate lines:
> x <- 1 > y <- 2 > z <- 3
Alternatively, you can place them on the same line, separated by semicolons:
> x <- 1; y <- 2; z <- 3
Parentheses
The parentheses notation returns the result of evaluating the expression inside the parentheses:
(expression
)
The operator has the same precedence as a function call. In fact, grouping a set of expressions inside parentheses is equivalent to evaluating a function of one argument that just returns its argument:
> 2 * (5 + 1) [1] 12 > # equivalent expression > f <- function (x) x > 2 * f(5 + 1) [1] 12
Grouping expressions with parentheses can be used to override the default order of operations. For example:
> 2 * 5 + 1 [1] 11 > 2 * (5 + 1) [1] 12
Curly Braces
Curly braces are used to evaluate a series of expressions (separated by new lines or semicolons) and return only the last expression:
{expression_1
;expression_2
; ...expression_n
}
Often, curly braces are used to group a set of operations in the body of a function:
> f <- function() {x <- 1; y <- 2; x + y} > f() [1] 3
However, curly braces can also be used as expressions in other contexts:
> {x <- 1; y <- 2; x + y} [1] 3
The contents of the curly braces are evaluated inside the current environment; a new environment is created by a function call but not by the use of curly braces:
> # when evaluated in a function, ...
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