histogram: Histograms and Kernel Density Plots

Description

Draw Histograms and Kernel Density Plots, possibly conditioned on other variables.

Usage

histogram(formula,
          data, 
          type = c("percent", "count", "density"),
          nint = if(is.factor(x)) length(levels(x))
                 else round(log2(length(x))+1),
          endpoints = range(x[!na.x]),
          breaks = if(is.factor(x)) seq(0.5, length = length(levels(x))
          + 1) else do.breaks(endpoints, nint),
          equal.widths = FALSE, 
          ...)
densityplot(formula, data, n = 50, plot.points = TRUE, ref = FALSE,
            ...)
do.breaks(endpoints, nint)

Arguments

formula

A formula of the form ~ x | g1 * g2 * ... indicates that histograms or Kernel Density estimates of x should be produced conditioned on the levels of the (optional) variables g1,g2,.... When the conditioni

data

optional data frame in which variables are to be evaluated

type

Character string indicating type of histogram to be drawn. ``percent'' and ``count'' give relative frequency and frequency histograms, and can be misleading when breakpoints are not equally spaced. ``density'' produces a density scale histogra

nint

Number of bins. Applies only when breaks is unspecified in the call.

endpoints

vector of length 2 indicating the range of x-values that is to be covered by the histogram. Again, applies only when breaks is unspecified. In do.breaks, this specifies the interval that is to be divided up.

breaks

numeric vector of length = (number of bins + 1) defining the breakpoints of the bins. Note that when breakpoints are not equally spaced, the only value of type that makes sense is density.

Usually all panels use the same brea

equal.widths

logical, relevant only when breaks=NULL. If TRUE, equally spaced bins will be selected, otherwise, approximately equal area bins will be selected (this would mean that the breakpoints will not be equally space

number of points at which density is to be evaluated

plot.points

logical specifying whether the x values should be plotted along the y=0 line.

ref

logical specifying whether a reference x-axis should be drawn.

...

other arguments, passed along to the panel function. In the case of densityplot, if the default panel function is used, then arguments appropriate to density can be included. This can control the details of how the Ke

Value

An object of class ``trellis''. The `update' method can be used to update components of the object and the `print' method (usually called by default) will plot it on an appropriate plotting device.

synopsis

histogram(formula, data = parent.frame(), allow.multiple = is.null(groups) || outer, outer = FALSE, auto.key = FALSE, aspect = "fill", panel = "panel.histogram", prepanel = NULL, scales = list(), strip = TRUE, groups = NULL, xlab, xlim, ylab, ylim, type = c("percent", "count", "density"), nint = if (is.factor(x)) length(levels(x)) else round(log2(length(x)) + 1), endpoints = extend.limits(range(x[!is.na(x)]), prop = 0.04), breaks = if (is.factor(x)) seq(0.5, length = length(levels(x))+1) else do.breaks(endpoints, nint), equal.widths = TRUE, drop.unused.levels, ..., default.scales, subscripts = !is.null(groups), subset = TRUE) densityplot(formula, data = parent.frame(), allow.multiple = is.null(groups) || outer, outer = FALSE, auto.key = FALSE, aspect = "fill", panel = if (is.null(groups)) "panel.densityplot" else "panel.superpose", prepanel = NULL, scales = list(), strip = TRUE, groups = NULL, xlab, xlim, ylab, ylim, bw = NULL, adjust = NULL, kernel = NULL, window = NULL, width = NULL, give.Rkern = FALSE, n = 50, from = NULL, to = NULL, cut = NULL, na.rm = NULL, drop.unused.levels, ..., default.scales, panel.groups = "panel.densityplot", subscripts = !is.null(groups), subset = TRUE)

Details

histogram draws Conditional Histograms, while densityplot draws Conditional Kernel Density Plots. The density estimate in densityplot is actually calculated using the function density, and all arguments accepted by it can be passed (as ...) in the call to densityplot to control the output. See documentation of density for details. (Note: The default value of the argument n of density is changed to 50.) These and all other high level Trellis functions have several arguments in common. These are extensively documented only in the help page for xyplot, which should be consulted to learn more detailed usage.

do.breaks is an utility function that calculates breakpoints given an interval and the number of pieces to break it into.

Examples

Run this code

require(stats)
histogram( ~ height | voice.part, data = singer, nint = 17,
          endpoints = c(59.5, 76.5), layout = c(2,4), aspect = 1,
          xlab = "Height (inches)")

histogram( ~ height | voice.part, data = singer,
          xlab = "Height (inches)", type = "density",
          panel = function(x, ...) {
              panel.histogram(x, ...)
              panel.mathdensity(dmath = dnorm, col = "black",
                                args = list(mean=mean(x),sd=sd(x)))
          } )

densityplot( ~ height | voice.part, data = singer, layout = c(2, 4),  
            xlab = "Height (inches)", bw = 5)

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