[Rd] xy.coords

[Duncan Murdoch]

On 12/31/2005 3:26 PM, Gabor Grothendieck wrote:
> I think this is just playng with words.  

I'm starting to be convinced of that by the fact that you haven't posted 
any sample code where using a single parameter would be desirable.

The fact that its always been
> like that is not sufficient and is not related to consistency.
> xyz.coords also does not work in accordance with the help file
> so the fact that the error extends to it just means they are both
> in error.

> 
> Modularity means loose coupling -- i.e. a function should be
> as independent as possible from its surroundings.  The fact
> that the second argument is not missing in uses within R base
> is not a valid argument for appropriate attention to this principle.
> 
> Furthermore, its clear that the current way it works is not even
> the intended way -- the intended and better way is as documented
> and the software, not the documentation, ought to be changed.

Take a look at the examples.  It's pretty clear that it is working as 
intended, and the documentation incorrectly says "missing" where it 
means "NULL".

Duncan Murdoch
> 
> 
> On 12/31/05, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
> 
>>On 12/31/2005 12:57 PM, Gabor Grothendieck wrote:
>>
>>>It does not achieve design consistency.
>>
>>It's consistent with the way it has been for at least 7 years, and is
>>consistent with xyz.coords().
>>
>>One would have to
>>
>>>specify NULL but that should not really be necessary.
>>
>>In fact, one almost never needs to specify NULL there.  It's the default
>>value for y in the high level functions that call xy.coords, so it is
>>put there automatically.
>>
>>Duncan Murdoch
>>
>>
>>>On 12/31/05, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
>>>
>>>
>>>>On 12/31/2005 12:21 PM, Gabor Grothendieck wrote:
>>>>
>>>>
>>>>>I think the point is that (1) it does not work as documented and (2) in
>>>>>most functions one can omit unnecessary args without having
>>>>>to specify NULL so its behvaior seems inconsistent from a design
>>>>>viewpoint.  By allowing either missing or NULL it will work as documented,
>>>>>and probably intended, yet continue to be backward compatible with
>>>>>existing usages.
>>>>
>>>>But a simpler change is to change the documentation, and it achieves all
>>>>of those objectives.
>>>>
>>>>Duncan Murdoch
>>>>
>>>>
>>>>>On 12/31/05, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
>>>>>
>>>>>
>>>>>
>>>>>>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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>>
>>
> 
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