histogram              package:lattice              R Documentation

Histograms and Kernel Density Plots

Description:

     Draw Histograms and Kernel Density Plots

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,
                 ...)

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 conditioning variables
          'g1,g2,...' are missing, the leading '~' can be dropped.

          'x' can be numeric (or factor for 'histogram'), and each of
          'g1,g2,...' must be either factors or shingles.

          As a special case, the right hand side of the formula ('x')
          can actually contain more than one variable separated by a
          '+' sign. What happens in this case is described in details
          in the documentation for 'xyplot'. 

    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
          histogram.

          'type' defaults to ``percent'', except when the breakpoints
          are unequally spaced or 'breaks = NULL', when it defaults to
          ``density''. 

    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. 

  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 breakpoints. This can be
          changed by specifying 'breaks = NULL'. This has the effect of
          letting each panel choose its own breakpoints. The choice of
          these breakpoints are made as follows: The number of bins is
          calculated by the formula for 'nint' above, and then
          breakpoints are chosen according to the value of
          'equal.widths'. 

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 spaced). 

       n: number of points at which density is to be evaluated

plot.points: logical specifying whether the 'x' values should be
          plotted. 

     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 Kernel Density Estimates
          are calculated. See documentation for 'density' for details. 

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.

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.

Note:

     The form of the arguments accepted by the default panel function
     'panel.histogram' is different from that in S-PLUS. Whereas S-PLUS
     calculates the heights inside 'histogram' and passes only the
     breakpoints and the heights to the panel function, here the
     original variable 'x' is passed along with the breakpoints. This
     allows plots as in the second example below.

Author(s):

     Deepayan Sarkar deepayan@stat.wisc.edu

See Also:

     'xyplot', 'panel.histogram', 'density', 'panel.densityplot',
     'panel.mathdensity', 'Lattice'

Examples:

     require(stats)
     data(singer)

     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)

