

   CCoonnddiittiioonniinngg PPlloottss

        coplot(formula, data, given.values, panel = points, rows, columns,
               show.given = TRUE, col = par("fg"), pch = par("pch"), ...)
        co.intervals(x, number = 6, overlap = 0.5)

   AArrgguummeennttss::

    formula: a formula describing the form of conditioning
             plot.  A formula of the form `y ~ x | a' indicates
             that plots of `y' versus `x' should be produced
             conditional on the variable `a'.  A formula of the
             form `y ~ x| a * b' indicates that plots of `y'
             versus `x' should be produced conditional on the
             two variables `a' and `b'.

             `x' and lang(y) must be numeric, but `a' and `b'
             may be either numeric or factors.

       data: a data frame containing values for any variables
             in the formula.  By default the environment where
             `coplot' was called from is used.

   given.values: a value or list of two values which determine
             how the conditioning on `a' and `b' is to take
             place.  Usually this is a matrix with two columns
             which each row of which gives and interval, to be
             conditioned on, but is can also be a single vector
             of numbers or a set of factor levels (if the vari-
             able being conditioned on is a factor).

      panel: a function which gives the action to be carried
             out in each panel of the display.  The default is
             `points'.

       rows: the panels of the plot are laid out in a `rows' by
             `columns' array.  `rows' gives the number of rows
             in the array.

    columns: the number of columns in the panel layout array.

   show.given: should conditioning plots be shown for the con-
             ditioning variables (default `TRUE')

        col: a vector of colors to be used to plot the points.
             If too short, the values are recycled.

        pch: a vector of plotting symbols or characters.  If
             too short, the values are recycyled.

        ...: additional arguments to the panel function.

     number: the number conditioning intervals.

    overlap: the fraction of overlap of the conditioning vari-
             ables.

   DDeessccrriippttiioonn::

        This function produces two variants of the conditioning
        plots discussed in the reference below.

   RReeffeerreenncceess::

        Cleveland, W. S. (1993).  Visualizing Data.  New Jer-
        sey: Summit Press.

   SSeeee AAllssoo::

        `pairs', `panel.smooth', `points'.

   EExxaammpplleess::

        ## Tonga Trench Earthquakes
        data(quakes)
        coplot(long ~ lat | depth, data = quakes)
        coplot(long ~ lat | depth * mag, data = quakes)

