substitute {base} | R Documentation |

`substitute`

returns the parse tree for the (unevaluated)
expression `expr`

, substituting any variables bound in
`env`

.

`quote`

simply returns its argument. The argument is not evaluated
and can be any R expression.

substitute(expr, env) quote(expr)

`expr` |
Any syntactically valid R expression |

`env` |
An environment or a list object. Defaults to the current evaluation environment. |

The typical use of `substitute`

is to create informative labels
for data sets and plots.
The `myplot`

example below shows a simple use of this facility.
It uses the functions `deparse`

and `substitute`

to create labels for a plot which are character string versions
of the actual arguments to the function `myplot`

.

Substitution takes place by examining each component of the parse tree
as follows: If it is not a bound symbol in `env`

, it is
unchanged. If it is a promise object, i.e., a formal argument to a
function or explicitly created using `delayedAssign()`

,
the expression slot of the promise replaces the symbol. If it is an
ordinary variable, its value is substituted, unless `env`

is
`.GlobalEnv`

in which case the symbol is left unchanged.

`substitute`

is a primitive function so positional matching is
used and names of supplied arguments are ignored.

The `mode`

of the result is generally `"call"`

but
may in principle be any type. In particular, single-variable
expressions have mode `"name"`

and constants have the
appropriate base mode.

Substitute works on a purely lexical basis. There is no guarantee that the resulting expression makes any sense.

Substituting and quoting often causes confusion when the argument is
`expression(...)`

. The result is a call to the
`expression`

constructor function and needs to be evaluated
with `eval`

to give the actual expression object.

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
*The New S Language*.
Wadsworth & Brooks/Cole.

`missing`

for argument “missingness”,
`bquote`

for partial substitution,
`sQuote`

and `dQuote`

for adding quotation
marks to strings.

(s.e <- substitute(expression(a + b), list(a = 1))) #> expression(1 + b) (s.s <- substitute( a + b, list(a = 1))) #> 1 + b c(mode(s.e), typeof(s.e)) # "call", "language" c(mode(s.s), typeof(s.s)) # (the same) # but: (e.s.e <- eval(s.e)) #> expression(1 + b) c(mode(e.s.e), typeof(e.s.e)) # "expression", "expression" substitute(x <- x + 1, list(x=1)) # nonsense myplot <- function(x, y) plot(x, y, xlab=deparse(substitute(x)), ylab=deparse(substitute(y))) ## Simple examples about lazy evaluation, etc: f1 <- function(x, y = x) { x <- x + 1; y } s1 <- function(x, y = substitute(x)) { x <- x + 1; y } s2 <- function(x, y) { if(missing(y)) y <- substitute(x); x <- x + 1; y } a <- 10 f1(a)# 11 s1(a)# 11 s2(a)# a typeof(s2(a))# "symbol"

[Package *base* version 2.2.1 Index]