| Type: | Package |
| Title: | Manipulate Virtual Functions |
| Version: | 1.0 |
| Depends: | R (≥ 4.2.0) |
| Suggests: | testthat, knitr, rmarkdown, onion |
| Maintainer: | Robin K. S. Hankin <hankin.robin@gmail.com> |
| Description: | If f <- function(x){x^2} and g <- function(x){x+1} it is a constant source of annoyance that "f+g" is not defined. Package 'vfunc' allows you to do this, and we have (f+g)(2) returning 5. The other arithmetic operators are similarly implemented. A wide class of coding bugs is eliminated. |
| License: | GPL-2 |
| Imports: | methods |
| VignetteBuilder: | knitr |
| NeedsCompilation: | no |
| Packaged: | 2025-07-25 10:18:52 UTC; rhankin |
| Author: | Robin K. S. Hankin
 [aut, cre] |
| Repository: | CRAN |
| Date/Publication: | 2025-07-28 18:50:02 UTC |
Manipulate Virtual Functions
Description
If f <- function(x){x^2} and g <- function(x){x+1} it is a
constant source of annoyance to me that “f+g” is not
defined. Package vfunc allows you to do this.
Details
The package defines a single S4 class, vf. This has a
single slot, .Data, of type function which means that
vf objects inherit much of the behaviour of functions, but for
which new methods (such as the Arith group of S4 generics)
may be defined.
Documentation Index
Index of help topics:
Compare-methods 'Compare' methods for 'vf' objects
Math Math group generic functions in the 'vfunc'
package: trig, exponential, log, etc.
Math-methods Methods for Function 'Math', 'Arith' in the
'vfunc' package
as.vf Coerce functions to a virtual function.
pow Iterated functions; functional powers
vf-class Class '"vf"'
vfunc-package Manipulate Virtual Functions
Author(s)
Robin K. S. Hankin [aut, cre] (ORCID: <https://orcid.org/0000-0001-5982-0415>)
Maintainer: Robin K. S. Hankin <hankin.robin@gmail.com>
Examples
f <- as.vf(function(x){x^2})
f + Sin
as.function(f*Sin + Exp)(1:4)
Compare methods for vf objects
Description
Wouldn't it be nice to say (f > g)(x) rather than the terrible,
tedious and error-prone f(x) > g(x)? Well, now you can!
Methods
signature(e1 = "ANY", e2 = "vf")signature(e1 = "function", e2 = "vf")signature(e1 = "vf", e2 = "ANY")signature(e1 = "vf", e2 = "function")signature(e1 = "vf", e2 = "vf")
Examples
x <- seq(from=0, to=2*pi, len=100)
(Sin > Cos*Tan)(x)
Math group generic functions in the vfunc package: trig, exponential, log, etc.
Description
The S4 Math group contains 35 functions including
sin(), log(), etc. The vfunc equivalents are
capitalized, as in Sin(), Log(), etc.
Usage
Abs(x)
Sign(x)
Sqrt(x)
Ceiling(x)
Floor(x)
Trunc(x)
Cummax(x)
Cummin(x)
Cumprod(x)
Cumsum(x)
Log(x)
Log10(x)
Log2(x)
Log1p(x)
Acos(x)
Acosh(x)
Asin(x)
Asinh(x)
Atan(x)
Atanh(x)
Exp(x)
Expm1(x)
Cos(x)
Cosh(x)
Cospi(x)
Sin(x)
Sinh(x)
Sinpi(x)
Tan(x)
Tanh(x)
Tanpi(x)
Gamma(x)
Lgamma(x)
Digamma(x)
Trigamma(x)
Arguments
x |
Generally take a single argument of class |
Details
The reason for this rather untransparent device is that primitive
functions such as sin() behave somewhat differently from other
functions. We have:
Sin <- as.vf(function(x){sin(x)})
setMethod("sin", "vf", function(x){as.vf(function(o){Sin(x(o))})})
We define Sin() to be an object of class vf; the call to
setMethod() ensures that Sin(f) operates as intended.
Value
Given a numeric, return a numeric; given a vf, return a vf
Note
Note that “sin <- as.vf(sin)” does not work as desired,
giving a runtime error; trying to get round this with things like
“sin <- as.vf(function(x)sin)” and similar means that
“sin(3)” does not work.
There is no way to inform all vf objects that, if used as a
function with an argument of a primitive such as sin, to return
another vf object—and not to try and evaluate
“f(sin)”, which fails:
f <- as.vf(function(x){x^2 + 1})
f(Sin)
#> An object of class "vf"
#> function (...)
#> {
#> e1(...) + e2
#> }
#> <bytecode: 0x6065e7c8a900>
#> <environment: 0x6065e7c8a548>
f(sin)
#> Error in x^2: non-numeric argument to binary operator
Above, we see f(sin) returning an error (it tries to evaluate
“sin^2 + 1”). Observe that “Sin^2 + 1” is
perfectly OK, for Sin is a virtual function.
Author(s)
Robin K. S. Hankin
Examples
Sin + Exp
c((Sin + Exp)(.02232) ,sin(0.02232) + exp(0.02232))
Methods for Function Math, Arith in
the vfunc package
Description
Various S4 methods to work with vf objects.
Comparison methods are documented at Compare-methods.
Coerce functions to a virtual function.
Description
Coerce objects to a virtual function. Numeric or complex arguments are coerced to a constant function.
Usage
as.vf(x)
Arguments
x |
Generally, a function or numeric |
Value
Returns an object of class vf.
Note
It is rarely necessary to coerce objects such as vectors or matrices
to class vf because the Arith methods operate on objects of
class ANY directly.
Author(s)
Robin K. S. Hankin
Examples
as.vf(\(x)x^2)
Sin + as.vf(\(p){p^3})
as.vf(1:10)(1e99)
Iterated functions; functional powers
Description
Given a function f\colon X\longrightarrow X, we define
f^0 = \mathrm{id_X}
f^{n+1} = f\circ f^n=f^n\circ f,\qquad n\geqslant 0
This gives us f^{n+m}=f^n\circ f^m and
\left(f^m\right)^n=f^{mn}, which motivates the notation.
For example, \sin^3=\sin\circ\sin\circ\sin, so
\sin^3(x)=\sin(\sin(\sin x)).
The operator is well-defined due to the power associativity of function composition.
Usage
pow(x, n)Arguments
x |
Object of class |
n |
Non-negative integer |
Value
Returns an object of class vf
Note
There are possibly more efficient methods requiring fewer
compositions, e.g. pow(f,9) (which would require 8 function
compositions) could be evaluated by pow(pow(f,3),3) (which
requires only four). But I am not sure that this would actually be
any faster, and I have not got round to thinking about it yet.
Also, package idiom for the caret “^” is reserved for
arithmetic exponentiation [so, for example, (f^3)(x) ==
f(x)*f(x)*f(x)]. I believe this is sub-optimal but was unable to
overload the caret to implement functional iteration.
Author(s)
Robin K. S. Hankin
Examples
pow(Sin,5)
Sin^5
f <- as.vf(function(x){x^2+1})
pow(f + Sin,4)
pow(f + Sin,4)(2)
Class "vf"
Description
Class vf stands for “virtual function”
Objects from the Class
Objects can be created by calls of the form new("vf", ...).
Slots
.Data:Object of class
"function"
Methods
- Arith
signature(e1 = "function", e2 = "vf"): ...- Arith
signature(e1 = "ANY", e2 = "vf"): ...- Arith
signature(e1 = "vf", e2 = "function"): ...- Arith
signature(e1 = "vf", e2 = "missing"): ...- Arith
signature(e1 = "vf", e2 = "ANY"): ...- Arith
signature(e1 = "vf", e2 = "vf"): ...- as.function
signature(x = "vf"): ...- as.vf
signature(x = "vf"): ...- coerce
signature(from = "function", to = "vf"): ...- coerce
signature(from = "ANY", to = "vf"): ...- coerce
signature(from = "vf", to = "function"): ...- Compare
signature(e1 = "function", e2 = "vf"): ...- Compare
signature(e1 = "ANY", e2 = "vf"): ...- Compare
signature(e1 = "vf", e2 = "function"): ...- Compare
signature(e1 = "vf", e2 = "ANY"): ...- Compare
signature(e1 = "vf", e2 = "vf"): ...- Math
signature(x = "vf"): ...
Author(s)
Robin K. S. Hankin
Examples
showClass("vf")