qq                  package:lattice                  R Documentation

Quantile-Quantile Plots of Two Samples

Description:

     Quantile-Quantile plots for comparing two Distributions

Usage:

     qq(x, data, ...)

     ## S3 method for class 'formula':
     qq(x, data, aspect = "fill", 
         panel = lattice.getOption("panel.qq"),
         prepanel, scales, strip, 
         groups, xlab, xlim, ylab, ylim, f.value = NULL, 
         drop.unused.levels = lattice.getOption("drop.unused.levels"),
         ...,
         lattice.options = NULL,
         qtype = 7,
         default.scales = list(),
         subscripts,
         subset)

Arguments:

       x: The object on which method dispatch is carried out.

          For the formula method, a formula of the form 'y ~ x | g1 *
          g2 * ...', where 'x' must be a numeric, and 'y' can be a
          factor, shingle, character or numeric vector, with the
          restriction that there must be exactly two levels of 'y',
          which divide the values of 'x' into two groups. Quantiles for
          these groups will be plotted along the two axes. 

    data: For the 'formula' methods, an optional data frame in which
          variables in the formula (as well as 'groups' and 'subset',
          if any) are to be evaluated. 

 f.value: optional numeric vector of probabilities, quantiles
          corresponding to which should be plotted.  Can also be a
          function of a single integer (representing sample size) that
          returns such a numeric vector.  The typical value for this
          argument is the function 'ppoints', which is also the S-PLUS
          default.  If specified, the probabilities generated by this
          function is used for the plotted quantiles, using the
          'quantile' function.

          'f.value' defaults to 'NULL', which is equivalent to using
          'function(n) ppoints(n, a = 1)'. This has the effect of
          including the minimum and maximum data values in the computed
          quantiles. This is similar to what happens for 'qqplot' but
          different from the default 'qq' behaviour in S-PLUS.

          For large data, this argument can be useful in plotting a
          smaller set of quantiles, which is usually enough to capture
          the pattern. 

   panel: The function that uses the packet (subset of display
          variables) corresponding to a panel to create a display. 
          Default panel functions are documented separately, and often
          have arguments that can be used to customize its display in
          various ways.  Such arguments can usually be directly
          supplied to the high level function.  

   qtype: 'type' argument for the 'quantile' 

aspect, prepanel, scales,
strip, groups, xlab, xlim, ylab, ylim, drop.unused.levels,
lattice.options, default.scales, subscripts, subset: 
          See 'xyplot' 

     ...: Further arguments.  See corresponding entry in 'xyplot' for
          non-trivial details. 

Details:

     'qq' produces a Q-Q plot of two samples.  The default behaviour of
     'qq' is different from the corresponding S-PLUS function. See the
     entry for 'f.value' for specifics.

     This 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.

Author(s):

     Deepayan Sarkar Deepayan.Sarkar@R-project.org

See Also:

     'xyplot', 'panel.qq', 'qqmath', 'Lattice'

Examples:

     qq(voice.part ~ height, aspect = 1, data = singer,
        subset = (voice.part == "Bass 2" | voice.part == "Tenor 1"))

