# fv

##### Create a Function Value Table

Advanced Use Only.
This low-level function creates an object of class `"fv"`

from raw numerical data.

##### Usage

```
fv(x, argu = "r", ylab = NULL, valu, fmla = NULL, alim = NULL,
labl = names(x), desc = NULL, unitname = NULL, fname = NULL, yexp = ylab)
```

##### Arguments

- x
A data frame with at least 2 columns containing the values of the function argument and the corresponding values of (one or more versions of) the function.

- argu
String. The name of the column of

`x`

that contains the values of the function argument.- ylab
Either

`NULL`

, or an R language expression representing the mathematical name of the function. See Details.- valu
String. The name of the column of

`x`

that should be taken as containing the function values, in cases where a single column is required.- fmla
Either

`NULL`

, or a`formula`

specifying the default plotting behaviour. See Details.- alim
Optional. The default range of values of the function argument for which the function will be plotted. Numeric vector of length 2.

- labl
Optional. Plot labels for the columns of

`x`

. A vector of strings, with one entry for each column of`x`

.- desc
Optional. Descriptions of the columns of

`x`

. A vector of strings, with one entry for each column of`x`

.- unitname
Optional. Name of the unit (usually a unit of length) in which the function argument is expressed. Either a single character string, or a vector of two character strings giving the singular and plural forms, respectively.

- fname
Optional. The name of the function itself. A character string.

- yexp
Optional. Alternative form of

`ylab`

more suitable for annotating an axis of the plot. See Details.

##### Details

This documentation is provided
for experienced programmers who want to modify the internal
behaviour of spatstat. Other users please see `fv.object`

.

The low-level function `fv`

is used to create an object of
class `"fv"`

from raw numerical data.

The data frame `x`

contains the numerical data.
It should have one column
(typically but not necessarily named `"r"`

)
giving the values of the function argument for which
the function has been evaluated; and at least one other column,
containing the corresponding values of the function.

Typically there is more than one column of function values. These columns typically give the values of different versions or estimates of the same function, for example, different estimates of the \(K\) function obtained using different edge corrections. However they may also contain the values of related functions such as the derivative or hazard rate.

`argu`

specifies the name of the column of
`x`

that contains the values of the function argument
(typically `argu="r"`

but this is not compulsory).

`valu`

specifies the name of another column
that contains the ‘recommended’ estimate of the function.
It will be used to provide function values in those situations where
a single column of data is required. For example,
`envelope`

computes its simulation envelopes
using the recommended value of the summary function.

`fmla`

specifies the default plotting behaviour.
It should be a formula, or a string that can be converted to a
formula. Variables in the formula are names of columns of `x`

.
See `plot.fv`

for the interpretation of this
formula.

`alim`

specifies the recommended range of the
function argument. This is used in situations where statistical
theory or statistical practice indicates that the computed
estimates of the function are not trustworthy outside a certain
range of values of the function argument. By default,
`plot.fv`

will restrict the plot to this range.

`fname`

is a string giving the name of the function itself.
For example, the \(K\) function would have `fname="K"`

.

`ylab`

is a mathematical expression
for the function value, used when labelling an axis
of the plot, or when printing a description of the
function. It should be an R language object.
For example the \(K\) function's mathematical name \(K(r)\) is rendered
by `ylab=quote(K(r))`

.

If `yexp`

is present, then `ylab`

will be
used only for printing, and `yexp`

will be used for
annotating axes in a plot. (Otherwise `yexp`

defaults to `ylab`

).
For example the cross-type \(K\) function
\(K_{1,2}(r)\) is rendered by something like
`ylab=quote(Kcross[1,2](r))`

and
`yexp=quote(Kcross[list(1,2)](r))`

to get the most satisfactory behaviour.

(A useful tip: use `substitute`

instead of
`quote`

to insert values of variables into an expression,
e.g. `substitute(Kcross[i,j](r), list(i=42,j=97))`

yields the same as `quote(Kcross[42, 97](r))`

.)

`labl`

is a character vector specifying plot labels
for each column of `x`

. These labels will appear on the
plot axes (in non-default plots), legends and printed output.
Entries in `labl`

may contain the string `"%s"`

which will be replaced
by `fname`

. For example the border-corrected estimate
of the \(K\) function has label `"%s[bord](r)"`

which
becomes `"K[bord](r)"`

.

`desc`

is a character vector containing intelligible
explanations of each column of `x`

. Entries in
`desc`

may contain the string `"%s"`

which will be replaced
by `ylab`

. For example the border correction estimate of the
\(K\) function has description `"border correction estimate of %s"`

.

##### Value

An object of class `"fv"`

, see `fv.object`

.

##### See Also

See `plot.fv`

for plotting an `"fv"`

object.

See `as.function.fv`

to convert an `"fv"`

object
to an R function.

Use `cbind.fv`

to combine several `"fv"`

objects.
Use `bind.fv`

to glue additional columns onto an existing
`"fv"`

object.

Use `range.fv`

to compute the range of \(y\) values
for a function, and `with.fv`

for more complicated
calculations.

The functions `fvnames`

, `fvnames<-`

allow the user to
use standard abbreviations to refer to columns of an `"fv"`

object.

*Undocumented* functions for modifying an `"fv"`

object
include `tweak.fv.entry`

and `rebadge.fv`

.

##### Examples

```
# NOT RUN {
df <- data.frame(r=seq(0,5,by=0.1))
df <- transform(df, a=pi*r^2, b=3*r^2)
X <- fv(df, "r", quote(A(r)),
"a", cbind(a, b) ~ r,
alim=c(0,4),
labl=c("r", "%s[true](r)", "%s[approx](r)"),
desc=c("radius of circle",
"true area %s",
"rough area %s"),
fname="A")
X
# }
```

*Documentation reproduced from package spatstat, version 1.55-1, License: GPL (>= 2)*