Thank you both for your helpful reply!  And apologies for the lack of a
reproducible example - I would/could send one now, but I believe Peter's
example will suffice (and thank you for that).  And making z a factor worked
perfectly.  Thank you!

Anthony

On Sun, Apr 25, 2010 at 10:20 AM, Peter Ehlers <ehlers@ucalgary.ca> wrote:

> Hi John,
>
> The problem seems to be with the order in which the 'levels' of
> the conditioning variable appear. Here's a reproducible example:
>
>  Prestige$tp<- with(Prestige, ifelse(type == "prof", 0, 1))
>
>  scatterplot(prestige ~ income | tp, data=Prestige)
>
> Note that I've just switched the 0/1 from your example.
>
> A quick look at scatterplot.formula suggests that wrapping
> the 'X[, 3]' in this line
>
>   scatterplot(X[, 2], X[, 1], groups = X[, 3], xlab = xlab,
>
> inside an as.factor() would solve the problem.
>
>  -Peter
>
>
>
> On 2010-04-25 8:40, John Fox wrote:
>
>> Dear Peter and Anthony,
>>
>> Thanks, Peter, for answering the question, but scatterplot() should work
>> even if z is not a factor, and does for me in the following example:
>>
>>  library(car)
>>> Prestige$tp<- with(Prestige, ifelse(type == "prof", 1, 0))
>>> scatterplot(prestige ~ income | tp, data=Prestige)
>>>
>>
>> So, Anthony, the usual advice about providing a reproducible example seems
>> applicable here.
>>
>> Regards,
>>  John
>>
>> --------------------------------
>> John Fox
>> Senator William McMaster
>>   Professor of Social Statistics
>> Department of Sociology
>> McMaster University
>> Hamilton, Ontario, Canada
>> web: socserv.mcmaster.ca/jfox
>>
>>
>>  -----Original Message-----
>>> From: r-help-bounces@r-project.org [mailto:r-help-bounces@r-project.org]
>>>
>> On
>>
>>> Behalf Of Peter Ehlers
>>> Sent: April-24-10 11:57 PM
>>> To: Anthony Lopez
>>> Cc: R-help@r-project.org
>>> Subject: Re: [R] categorical variable in scatterplot (car)
>>>
>>> On 2010-04-24 21:30, Anthony Lopez wrote:
>>>
>>>> Hello R folks,
>>>>
>>>> I am encountering a problem with the following scatterplot function from
>>>>
>>> the
>>>
>>>> car package:
>>>>
>>>>  scatterplot(y~x|z)
>>>>>
>>>>
>>>> where y and x are continuous (interval) random variables and z is a
>>>> categorical variable.  When z is a categorical variable coded 1 or 2, I
>>>> (appropriately) get a scatterplot of y by x, coded by z.  Similarly,
>>>>
>>> when z
>>
>>> is a categorical variable coded 1, 2, or 3, there is again, no problem.
>>>>   However, when z is a categorical variable coded 0 or 1, the
>>>>
>>> scatterplot
>>
>>>
>>>>  scatterplot(y~x|z)
>>>>>
>>>>
>>>> is exactly identical to the one generated by
>>>>
>>>>  scatterplot(y~x)
>>>>>
>>>>
>>>> It is not possible that this is due to the fact that there is no
>>>>
>>> difference
>>
>>> between the categories.  It is as if R doesn't "see" that I want it
>>>>
>>> coded
>>
>>> by
>>>
>>>> z.  But this only happens when one of the categories of z is coded "0"
>>>>
>>> (i.e.
>>>
>>>> zero).  Any ideas why this is so, or how I can fix this without recoding
>>>>
>>> my
>>
>>> variable?
>>>>
>>>
>>> Make z a factor (which it really should be anyway).
>>>
>>>   -Peter Ehlers
>>>
>>>
>>>> Thank you!
>>>>
>>>> Anthony
>>>>
>>>>        [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
>>>> R-help@r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide http://www.R-project.org/posting-
>>>>
>>> guide.html
>>>
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>
>>>>
>>>>
>>> --
>>> Peter Ehlers
>>> University of Calgary
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>>
>> http://www.R-project.org/posting-guide.html
>>
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>>
>>
>>
> --
> Peter Ehlers
> University of Calgary
>

	[[alternative HTML version deleted]]

