Create a function from a formula.

1 2 | ```
## S3 method for class 'formula'
as.function(x, ...)
``` |

`x` |
Formula with no left side. |

`...` |
Currently not used. |

A function is returned whose formal arguments are the
variables in the left hand side, whose body
is the expression on the right side of the formula and whose
environment is the environment of the formula. If there is
no left hand side the free variables on the right, in the
order encountered are used as the arguments. `letters`

,
`LETTERS`

and `pi`

are ignored and not used as arguments.
If there is no left hand side and
any of `..1`

, `..2`

, ..., `..9`

are found
as free variables then they are not used as arguments but `...`

is used as a trailing argument instead.
If there is no left hand side and ``&``

is found as a free variable
then that variable is used as the first argument and `...`

is added
as the last argument.
If the left hand side is `0`

then the function is created as
a zero argument function.

`->`

, `->>`

, `=`

, `<-`

, `<<-`

and `?`

all have lower operator precdence than `~`

so function bodies that
contain them typically must be surrounded with `{...}`

.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | ```
old.options <- options(keep.source = FALSE)
as.function(~ as.numeric(x) + as.numeric(y))
as.function(x + y ~ as.numeric(x) + as.numeric(y)) # same
as.function(~ ..1 + ..2)
# the replacement function in gsubfn uses as.function.formula to
# interpret formulas as functions. Here we insert ! after each digit.
gsubfn("[0-9]", ~ paste0(`&`, "!"), "ab4cd5")
## Not run:
# example where function body must be surrounded with {...}
# due to use of <<-. See warning section above.
assign("mywarn", NULL, .GlobalEnv)
fn$tryCatch( warning("a warning"),
warning = w ~ { mywarn <<- conditionMessage(w)})
print(mywarn)
## End(Not run)
options(old.options)
``` |

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