expression {base} | R Documentation |
Creates or tests for objects of mode "expression"
.
expression(...) is.expression(x) as.expression(x, ...)
... |
expression : R objects, typically calls, symbols
or constants.as.expression : arguments to be passed to methods. |
x |
an arbitrary R object. |
‘Expression’ here is not being used in its colloquial sense,
that of mathematical expressions. Those are calls (see
call
) in R, and an R expression vector is a list of
calls, symbols etc, typically as returned by parse
.
As an object of mode "expression"
is a list, it can be
subsetted by both [
and by [[
, the latter extracting
individual calls etc.
expression
and is.expression
are primitive functions.
expression
returns a vector of type "expression"
containing its arguments (unevaluated).
is.expression
returns TRUE
if expr
is an
expression object and FALSE
otherwise.
as.expression
attempts to coerce its argument into an
expression object. It is generic, and only the default method is
described here. NULL
, calls, symbols (see
as.symbol
) and pairlists are returned as the element of
a length-one expression vector. Vectors (including lists) are placed
element-by-element into an expression vector. Other types are not
currently supported.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
call
,
eval
,
function
.
Further,
text
and
legend
for plotting mathematical expressions.
length(ex1 <- expression(1+ 0:9))# 1 ex1 eval(ex1)# 1:10 length(ex3 <- expression(u,v, 1+ 0:9))# 3 mode(ex3 [3]) # expression mode(ex3[[3]])# call rm(ex3)