# eval.fv

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##### Evaluate Expression Involving Functions

Evaluates any expression involving one or more function value (fv) objects, and returns another object of the same kind.

Keywords
manip, spatial, programming
##### Usage
eval.fv(expr, envir)
##### Arguments
expr
An expression.
envir
Optional. The environment in which to evaluate the expression.
##### Details

This is a wrapper to make it easier to perform pointwise calculations with the summary functions used in spatial statistics.

An object of class "fv" is essentially a data frame containing several different statistical estimates of the same function. Such objects are returned by Kest and its relatives.

For example, suppose X is an object of class "fv" containing several different estimates of the Ripley's K function $K(r)$, evaluated at a sequence of values of $r$. Then eval.fv(X+3) effectively adds 3 to each function estimate in X, and returns the resulting object.

Suppose X and Y are two objects of class "fv" which are compatible (in particular they have the same vector of $r$ values). Then eval.im(X + Y) will add the corresponding function values in X and Y, and return the resulting function.

In general, expr can be any expression involving (a) the names of objects of class "fv", (b) scalar constants, and (c) functions which are vectorised. See the Examples.

First eval.fv determines which of the variable names in the expression expr refer to objects of class "fv". Each such name is replaced by a vector containing the function values. The expression is then evaluated. The result should be a vector; it is taken as the new vector of function values.

The expression expr must be vectorised. There must be at least one object of class "fv" in the expression. All such objects must be compatible.

##### Value

• Another object of class "fv".

fv.object, Kest

• eval.fv
##### Examples
# manipulating the K function
X <- rpoispp(42)
Ks <- Kest(X)

eval.fv(Ks + 3)
Ls <- eval.fv(sqrt(Ks/pi))

# manipulating two K functions
Y <- rpoispp(20)
Kr <- Kest(Y)

Kdif <- eval.fv(Ks - Kr)
Z <- eval.fv(sqrt(Ks/pi) - sqrt(Kr/pi))
Documentation reproduced from package spatstat, version 1.24-1, License: GPL (>= 2)

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