[Rd] xy.coords

[Duncan Murdoch]

On 12/30/2005 10:10 PM, Gabor Grothendieck wrote:
> 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) .

It would be better to change the docs to say "if 'y' is NULL ...".  The 
code has been the way it is for years and years, and is widely used.

Changing the test to missing(y) would mean all existing uses that put a 
NULL there would need to be changed.

Adding a default value of NULL to y would have less impact, but I'd 
still be worried about it having long-range bad effects.

Duncan Murdoch