Vectorize a Scalar Function

Description

Vectorize creates a function wrapper that vectorizes the action of its argument FUN.

Usage

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Vectorize(FUN, vectorize.args = arg.names, SIMPLIFY = TRUE,
          USE.NAMES = TRUE)

Arguments

FUN

function to apply, found via match.fun.

vectorize.args

a character vector of arguments which should be vectorized. Defaults to all arguments of FUN.

SIMPLIFY

logical or character string; attempt to reduce the result to a vector, matrix or higher dimensional array; see the simplify argument of sapply.

USE.NAMES

logical; use names if the first ... argument has names, or if it is a character vector, use that character vector as the names.

Details

The arguments named in the vectorize.args argument to Vectorize are the arguments passed in the ... list to mapply. Only those that are actually passed will be vectorized; default values will not. See the examples.

Vectorize cannot be used with primitive functions as they do not have a value for formals.

It also cannot be used with functions that have arguments named FUN, vectorize.args, SIMPLIFY or USE.NAMES, as they will interfere with the Vectorize arguments. See the combn example below for a workaround.

Value

A function with the same arguments as FUN, wrapping a call to mapply.

Examples

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# We use rep.int as rep is primitive
vrep <- Vectorize(rep.int)
vrep(1:4, 4:1)
vrep(times = 1:4, x = 4:1)

vrep <- Vectorize(rep.int, "times")
vrep(times = 1:4, x = 42)

f <- function(x = 1:3, y) c(x, y)
vf <- Vectorize(f, SIMPLIFY = FALSE)
f(1:3, 1:3)
vf(1:3, 1:3)
vf(y = 1:3) # Only vectorizes y, not x

# Nonlinear regression contour plot, based on nls() example
require(graphics)
SS <- function(Vm, K, resp, conc) {
    pred <- (Vm * conc)/(K + conc)
    sum((resp - pred)^2 / pred)
}
vSS <- Vectorize(SS, c("Vm", "K"))
Treated <- subset(Puromycin, state == "treated")

Vm <- seq(140, 310, length.out = 50)
K <- seq(0, 0.15, length.out = 40)
SSvals <- outer(Vm, K, vSS, Treated$rate, Treated$conc)
contour(Vm, K, SSvals, levels = (1:10)^2, xlab = "Vm", ylab = "K")

# combn() has an argument named FUN
combnV <- Vectorize(function(x, m, FUNV = NULL) combn(x, m, FUN = FUNV),
                    vectorize.args = c("x", "m"))
combnV(4, 1:4)
combnV(4, 1:4, sum)

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