qq                  package:lattice                  R Documentation

Quantile-Quantile Plots of Two Samples

Description:

     Quantile-Quantile plots for comparing two Distributions

Usage:

     qq(formula, f.value = NULL, ...)

Arguments:

 formula: 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. 

 f.value: optional function of a single integer (representing the
          larger of the two sample sizes), returning a vector of
          probabilities corresponding to which quantiles should be
          plotted. The typical value for this argument is '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. 

     ...: Other arguments

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@stat.wisc.edu

See Also:

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

Examples:

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

