[Rd] xy.coords

Duncan Murdoch murdoch at stats.uwo.ca
Sat Dec 31 18:01:55 CET 2005

On 12/31/2005 8:57 AM, Gabor Grothendieck wrote:
> It could be changed to missing(y) || is.null(y) and the docs amended.
> That way existing code will continue to work and code that otherwise
> gives an error currently, but should have worked, will now work too.

Can you give an example where you would want to use xy.coords(y ~ x)? 
Normally xy.coords() is used in other functions, and they can default y 
to NULL (see plot.default, for example).

Duncan Murdoch
> On 12/31/05, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
>>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

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