R help - Sep 2011 - Problems with aggregate() function in stats package

Hi,

I'm having some problems with the aggregate() function in the {stats} 
package, and the documentation doesn't address them.

1) Why would the first line work, but the second not? According to the 
help file, it accepts a "data=" argument.
>  with(tsrc, aggregate(x=DistRatio, by=list(Condition), FUN=mean))
     Group.1        x
1 Congruent 1.741789
2  Mismatch 1.771425
>  aggregate(x=DistRatio, by=list(Condition), data=tsrc, FUN=mean)
Error in aggregate(x = DistRatio, by = list(Condition), data = tsrc, FUN = mean)
:
   object 'DistRatio' not found


2) The subset argument also does not appear to work (perhaps this is the 
same issue?):
>  with(tsrc, aggregate(x=DistRatio, by=list(Condition),
subset=Drop!="Yes", FUN=mean))
     Group.1        x
1 Congruent 1.741789
2  Mismatch 1.771425
>  with(tsrc[tsrc$Drop!="Yes",], aggregate(x=DistRatio,
by=list(Condition), FUN=mean))
     Group.1        x
1 Congruent 1.700215
2  Mismatch 1.859795


So, am I doing something wrong or is this function just not working as 
advertised?

Thanks,

Jon

-- 
Jon Zadra
Department of Psychology
University of Virginia
P.O. Box 400400
Charlottesville VA 22904
(434) 982-4744
email: zadra at virginia.edu
<http://www.google.com/calendar/embed?src=jzadra%40gmail.com>

On Sep 15, 2011, at 4:07 PM, Jon Zadra wrote:
> Hi,
> 
> I'm having some problems with the aggregate() function in the {stats}
package, and the documentation doesn't address them.
> 
> 1) Why would the first line work, but the second not? According to the help
file, it accepts a "data=" argument.
> 
>> with(tsrc, aggregate(x=DistRatio, by=list(Condition), FUN=mean))
>    Group.1        x
> 1 Congruent 1.741789
> 2  Mismatch 1.771425
> 
>> aggregate(x=DistRatio, by=list(Condition), data=tsrc, FUN=mean)
> Error in aggregate(x = DistRatio, by = list(Condition), data = tsrc, FUN =
mean) :
>  object 'DistRatio' not found
> 
> 
> 2) The subset argument also does not appear to work (perhaps this is the
same issue?):
> 
>> with(tsrc, aggregate(x=DistRatio, by=list(Condition),
subset=Drop!="Yes", FUN=mean))
>    Group.1        x
> 1 Congruent 1.741789
> 2  Mismatch 1.771425
> 
>> with(tsrc[tsrc$Drop!="Yes",], aggregate(x=DistRatio,
by=list(Condition), FUN=mean))
>    Group.1        x
> 1 Congruent 1.700215
> 2  Mismatch 1.859795
> 
> 
> So, am I doing something wrong or is this function just not working as
advertised?
> 
> Thanks,
> 
> Jon


You are combining syntax from the data frame method for aggregate() with
arguments (data and subset) that are only available in the formula method. Be
sure to read the help page for the function and note at the top of the page, the
different syntax for each method. Of course, note the examples as well.

If you want to use the formula method with 'data' and 'subset'
you would need to use something like:

  aggregate(DistRatio ~ Condition, data = tsrc, FUN = mean)

or:

  aggregate(DistRatio ~ Condition, data = tsrc, subset = Drop !=
"Yes", FUN = mean)

HTH,

Marc Schwartz