[Rd] xy.coords

[Gabor Grothendieck]

In ?xy.coords it says:

     If 'y' is missing and 'x' is a

     formula: of the form 'yvar ~ xvar'. 'xvar' and 'yvar' are used as
          x and y variables.

     list: containing components 'x' and 'y', these are used to define
          plotting coordinates.

     time series: the x values are taken to be 'time(x)' and the y
          values to be the time series.

     matrix with two columns: the first is assumed to contain the x
          values and the second the y values.

however, in fact, if y is missing an error is given. e.g.

x <- 1:3
y <- 4:6
xy.coords(y ~ x) # error
xy.coords(cbind(x, y)) # error
xy.coords(ts(y)) # error

Looking at the code, is.null(y) in the first line of the
body should be missing(y) .