gplots: wapply – R documentation

Become an expert in R — Interactive courses, Cheat Sheets, certificates and more!

wapply

Compute the Value of a Function Over a Local Region Of An X-Y Plot

Description

This function applies the specified function to the sets of y values that are defined by overlapping "windows" in the x-dimension. For example, setting fun=mean returns local means, while setting fun=function(x) sqrt(var(x)) returns local estimates of the standard deviation.

Usage

wapply(x, y, fun=mean, method="range", width, n=50, drop.na=TRUE,
       pts, ...)

Arguments

`x`	vector of x values for (x,y) pairs
`y`	vector of y values for (x,y) pairs
`fun`	function to be applied
`method`	method of defining an x-neighborhood. One of "width","nobs","range", or "fraction". See details.
`width`	width of an x-neighborhood. See details.
`n`	Number of equally spaced points at which to compute local estimates. See details.
`drop.na`	should points which result in missing values `NA` be omitted from the return value. Defaults to true.
`pts`	`x` locations at which to compute the local mean when using the "width" or "range" methods. Ignored otherwise.
`...`	arguments to be passed to `fun`

Details

Two basic techniques are available for determining what points fall within the same x-neighborhood. The first technique uses a window with a fixed width in the x-dimension and is is selected by setting method="width" or method="range". For method="width" the width argument is an absolute distance in the x-dimension. For method="range", the width is expressed as a fraction of the x-range. In both cases, pts specifies the points at which evaluation of fun occurs. When pts is omitted, n x values equally spaced along the x range are used.

The second technique uses windows containing k neighboring points. The (x,y) pairs are sorted by the x-values and the nearest k/2 points with higher x values and the k/2 nearest points with lower x values are included in the window. When method="nobs", k equals width (actually 2*floor(width/2) ). When method="fraction", width specifies what fraction of the total number of points should be included. The actual number of points included in each window will be floor(n*frac/2)*2. Regardless of the value of pts, the function fun will be evaluated at all x locations.

Value

Returns a list with components

`x`	x location'
`y`	Result of applying `fun` to the window about each x location

Author(s)

Gregory R. Warnes greg@warnes.net

Examples

#show local mean and inner 2-sd interval to help diagnose changing mean
#or variance structure
x <- 1:1000
y <- rnorm(1000, mean=1, sd=1 + x/1000 )

plot(x,y)
lines(wapply(x,y,mean),col="red")

CL <- function(x,sd) mean(x)+sd*sqrt(var(x))

lines(wapply(x,y,CL,sd= 1),col="blue") 
lines(wapply(x,y,CL,sd=-1),col="blue") 
lines(wapply(x,y,CL,sd= 2),col="green")
lines(wapply(x,y,CL,sd=-2),col="green")

#show local mean and inner 2-sd interval to help diagnose changing mean
#or variance structure
x <- 1:1000
y <- rnorm(1000, mean=x/1000, sd=1)

plot(x,y)
lines(wapply(x,y,mean),col="red")

CL <- function(x,sd) mean(x)+sd*sqrt(var(x))

lines(wapply(x,y,CL,sd= 1,method="fraction",width=1/20),col="blue")
lines(wapply(x,y,CL,sd=-1,method="fraction",width=1/20),col="blue")
lines(wapply(x,y,CL,sd= 2,method="nobs",width=250),col="green")
lines(wapply(x,y,CL,sd=-2,method="nobs",width=250),col="green")

gplots

Various R Programming Tools for Plotting Data

v3.1.1

GPL-2

Authors

Gregory R. Warnes [aut], Ben Bolker [aut], Lodewijk Bonebakker [aut], Robert Gentleman [aut], Wolfgang Huber [aut], Andy Liaw [aut], Thomas Lumley [aut], Martin Maechler [aut], Arni Magnusson [aut], Steffen Moeller [aut], Marc Schwartz [aut], Bill Venables [aut], Tal Galili [ctb, cre]

Initial release

2020-11-28