xy.coords                package:base                R Documentation

Extracting Plotting Structures

Description:

     `xy.coords' is used by many function to obtain x and y coordinates
     for plotting. The use of this common mechanism across all R
     functions produces a measure of consistency.

     `plot.default' and `lowess' are examples of functions which use
     this mechanism.

Usage:

     xy.coords(x, y, xlab=NULL, ylab=NULL, log=NULL, recycle = FALSE)

Arguments:

     x,y: the x and y coordinates of a set of points. Alternatively, a
          single argument `x' can be be provided. In this case, an
          attempt is made to interpret the argument in a way suitable
          for plotting. If the argument is a formula  `yvar ~ xvar',
          `xvar' and `yvar' are used as x and y variables; if the
          argument is a list containing components `x' and `y', these
          are used are assumed to define plotting coordinates; if the
          argument contains a time series, the x values are taken to be
          time and the y values to be the time series; if the argument
          is a matrix with two columns, the first is assumed to contain
          the x values and the second the y values; in any other case,
          the argument is coerced to a vector and the values plotted
          against their indices.

xlab,ylab: names for the x and y variables to be extracted.

     log: character, `"x"', `"y"' or both, as for `plot'.  Sets
          negative values to `NA' and gives a warning.

 recycle: logical; if `TRUE', recycle (`rep') the shorter of `x' or `y'
          if their lengths differ.

Value:

     A list with the components 

       x: numeric (i.e. `"double"') vector of abscissa values.

       y: numeric vector of the same length as `x'.

    xlab: `character(1)' or `NULL', the `label' of `x'.

    ylab: `character(1)' or `NULL', the `label' of `y'.

Examples:

     xy.coords(fft(c(1:10)), NULL)
     data(cars) ; attach(cars)
     xy.coords(dist ~ speed, NULL)$xlab # = "speed"

     str(xy.coords(1:3, 1:2, recycle=TRUE))
     str(xy.coords(-2:10,NULL, log="y")) 
     ##> warning: 3 y values <=0 omitted ..

