# as.function.fv

##### Convert Function Value Table to Function

Converts an object of class `"fv"`

to an Rlanguage function.

##### Usage

```
## S3 method for class 'fv':
as.function(x, ..., value=".y", extrapolate=FALSE)
``` ## S3 method for class 'rhohat':
as.function(x, ..., value=".y", extrapolate=TRUE)

##### Arguments

- x
- Object of class
`"fv"`

or`"rhohat"`

. - ...
- Ignored.
- value
- Optional. Character string or character vector selecting
one or more of the columns of
`x`

for use as the function value. See Details. - extrapolate
- Logical, indicating whether to extrapolate the function
outside the domain of
`x`

. See Details.

##### Details

A function value table (object of class `"fv"`

)
is a convenient way of storing and plotting
several different estimates of the same function.
Objects of this class are returned
by many commands in `Kest`

which returns an estimate of Ripley's $K$-function
for a point pattern dataset.

Sometimes it is useful to convert the function value table
to a `function`

in the Rlanguage. This is done by
`as.function.fv`

. It converts an object `x`

of class `"fv"`

to an Rfunction `f`

.

If `f <- as.function(x)`

then `f`

is an Rfunction
that accepts a numeric argument and returns a corresponding value
for the summary function by linear interpolation between the values
in the table `x`

.

Argument values lying outside the range of the table
yield an `NA`

value (if `extrapolate=FALSE`

)
or the function value at the nearest endpoint of the range
(if `extrapolate = TRUE`

).
To apply different rules to the left and right extremes,
use `extrapolate=c(TRUE,FALSE)`

and so on.
Typically the table `x`

contains several columns of
function values corresponding to different edge corrections.
Auxiliary information for the table identifies one of these
columns as the *recommended value*.
By default, the values of the function `f <- as.function(x)`

are taken from this column of recommended values.
This default can be changed using the argument `value`

,
which can be a character string or character vector of names of
columns of `x`

. Alternatively `value`

can be one of
the abbreviations used by `fvnames`

.

If `value`

specifies a single column of the table,
then the result is a function `f(r)`

with a single numeric
argument `r`

(with the same name as the orginal argument
of the function table).

If `value`

specifies several columns of the table,
then the result is a function `f(r,what)`

where `r`

is the numeric argument and
`what`

is a character string identifying the column of values
to be used.

The formal arguments of the resulting function
are `f(r, what=value)`

, which
means that in a call to this function `f`

, the permissible values
of `what`

are the entries of the original vector `value`

;
the default value of `what`

is the first entry of `value`

.
The command `as.function.fv`

is a method for the generic command
`as.function`

.

##### Value

- A
`function(r)`

or`function(r,what)`

where`r`

is the name of the original argument of the function table.

##### See Also

##### Examples

```
K <- Kest(cells)
f <- as.function(K)
f
f(0.1)
g <- as.function(K, value=c("iso", "trans"))
g
g(0.1, "trans")
```

*Documentation reproduced from package spatstat, version 1.42-2, License: GPL (>= 2)*