Learn R Programming

lessR (version 2.8)

Density: Density Curves from Data plus Histogram

Description

Abbreviation: dn

Plots a normal density curve and/or a general density curve superimposed over a histogram, all estimated from the data. Also reports the Shapiro-Wilk normality test and summary statistics.

Usage

Density(x, data=mydata, 

bw="nrd0", type=c("both", "general", "normal"), bin.start=NULL, bin.width=NULL,

col.fill=getOption("col.fill.pt"), col.bg=getOption("col.bg"), col.grid=getOption("col.grid"),

col.nrm="black", col.gen="black", col.fill.nrm="transparent", col.fill.gen="transparent",

cex.axis=.85, col.axis="gray30", col.ticks="gray30", x.pt=NULL, xlab=NULL, main=NULL, y.axis=FALSE, x.min=NULL, x.max=NULL, band=FALSE,

quiet=FALSE, pdf.file=NULL, pdf.width=5, pdf.height=5, ...)

dn(...) den(...)

Arguments

x
Variable for which to construct the histogram and density plot.
data
Data frame that contains the variable of interest, default is mydata.
bw
Bandwidth of kernel estimation.
type
Type of density curve plotted. By default, both the general density and the normal density are plotted.
bin.start
Optional specified starting value of the bins.
bin.width
Optional specified bin width, which can be specified with or without a bin.start value.
col.fill
Default (for default color theme of "blue") is to display the histogram in a light gray. To suppress, the histogram, specify a color of "transparent".
col.bg
Color of the plot background.
col.grid
Color of the grid lines.
col.nrm
Color of the normal curve.
col.gen
Color of the general density curve.
col.fill.nrm
Fill color for the estimated normal curve, with a transparent blue as the default.
col.fill.gen
Fill color for the estimated general density curve, with a transparent light red as the default.
cex.axis
Scale magnification factor, which by default displays the axis values to be smaller than the axis labels.
col.axis
Color of the font used to label the axis values.
col.ticks
Color of the ticks used to label the axis values.
x.pt
Value of the point on the x-axis for which to draw a unit interval around illustrating the corresponding area under the general density curve. Only applies when requesting type=general.
xlab
Label for x-axis.
main
Title of graph.
y.axis
Specifies if the y-axis, the density axis, should be included.
x.min
Smallest value of the variable x plotted on the x-axis.
x.max
Largest value of the variable x plotted on the x-axis.
band
If TRUE, add a rug plot, a direct display of density in the form of a narrow band beneath the density curve
quiet
If set to TRUE, no text output.
pdf.file
Name of the pdf file to which graphics are redirected.
pdf.width
Width of the pdf file in inches.
pdf.height
Height of the pdf file in inches.
...
Other parameter values for graphics as defined processed by plot, including xlim, ylim, lwd and cex.lab, col.main, density

Details

OVERVIEW Results are based on the standard dnorm function and density R functions for estimating densities from data, as well as the hist function for calculating a histogram. Colors are provided by default and can also be specified.

The default histogram can be modified with the bin.start and bin.width options. Use the Histogram function in this package for more control over the parameters of the histogram.

The limits for the axes are automatically calculated so as to provide sufficient space for the density curves and histogram, and should generally not require user intervention. Also, the curves are centered over the plot window so that the resulting density curves are symmetric even if the underlying histogram is not. The estimated normal curve is based on the corresponding sample mean and standard deviation.

If x.pt is specified, then type is set to general and y.axis set to TRUE.

DATA If the variable is in a data frame, the input data frame has the assumed name of mydata. If this data frame is named something different, then specify the name with the data option. Regardless of its name, the data frame need not be attached to reference the variable directly by its name, that is, no need to invoke the mydata$name notation.

COLOR THEME Individual colors in the plot can be manipulated with options such as col.bars for the color of the histogram bars. A color theme for all the colors can be chosen for a specific plot with the colors option with the lessR function set. The default color theme is blue, but a gray scale is available with "gray", and other themes are available as explained in set, such as "red" and "green". Use the option ghost=TRUE for a black background, no grid lines and partial transparency of plotted colors.

VARIABLE LABELS If variable labels exist, then the corresponding variable label is by default listed as the label for the horizontal axis and on the text output. For more information, see Read.

PDF OUTPUT Because of the customized graphic windowing system that maintains a unique graphic window for the Help function, the standard graphic output functions such as pdf do not work with the lessR graphics functions. Instead, to obtain pdf output, use the pdf.file option, perhaps with the optional pdf.width and pdf.height options. These files are written to the default working directory, which can be explicitly specified with the R setwd function.

ONLY VARIABLES ARE REFERENCED The referenced variable in a lessR function can only be a variable name. This referenced variable must exist in either the referenced data frame, mydata by default, or in the user's workspace, more formally called the global environment. That is, expressions cannot be directly evaluated. For example:

> Density(rnorm(50)) # does NOT work}

Instead, do the following: > Y <- rnorm(50) # create vector Y in user workspace > Density(Y) # directly reference Y

[object Object],[object Object]

dnorm, density, hist, plot, rgb, shapiro.test.

# generate 100 random normal data values y <- rnorm(100)

# normal curve and general density curves superimposed over histogram # all defaults Density(y)

# short name dn(y)

# save the density plot to a pdf file Density(y, pdf.file="MyDensityPlot.pdf")

# suppress the histogram, leaving only the density curves # specify x-axis label per the xlab option for the plot function Density(y, col.bars="transparent", xlab="My Var")

# specify (non-transparent) colors for the curves, # to make transparent, need alpha option for the rgb function Density(y, col.nrm="darkgreen", col.gen="plum")

# display only the general estimated density # so do not display the estimated normal curve # specify the bandwidth for the general density curve, # use the standard bw option for the density function Density(y, type="general", bw=.6)

# display only the general estimated density and a corresponding # interval of unit width around x.pt Density(y, type="general", x.pt=2)

# create data frame, mydata, to mimic reading data with rad function # although data not attached, access the variable directly by its name mydata <- data.frame(rnorm(100)) names(mydata) <- "X" Density(X)

# variable of interest is in a data frame which is not the default mydata # access the breaks variable in the R provided warpbreaks data set # although data not attached, access the variable directly by its name data(warpbreaks) Density(breaks, data=warpbreaks)histogram density color