[R] aggregate vs tapply; is there a middle ground?

[Joseph LeBouton]

Thanks, Phil!  I've literally spent two hours on my own trying to find 
something that does exactly that.  Thanks for another pair of functions 
added to my (slowly!) growing R vocabulary.

-jlb

Phil Spector wrote:
> Joseph -
>    I'm sure there are clearer and more efficient ways to do it, but 
> here's something
> that seems to do what you want:
> 
> z = tapply(y,list(var1,var2,var3,var4),sum)
> data.frame(do.call('expand.grid',dimnames(z)),y=do.call('rbind',as.list(z))) 
> 
> 
>                                        - Phil Spector
>                      Statistical Computing Facility
>                      Department of Statistics
>                      UC Berkeley
>                      spector at stat.berkeley.edu
> 
> 
> On Sat, 11 Feb 2006, Joseph LeBouton wrote:
> 
>> Dear all,
>>
>> I'm wanting to do a series of comparisons among 4 categorical variables:
>>
>> a <- aggregate(y, list(var1, var2, var3, var4), sum)
>>
>> This gets me a very nice 2-dimensional data frame with one column per
>> variable, BUT, as help for aggregate says, <<empty subsets are
>> removed>>.  I don't see in help(aggregate) how I can change this.
>>
>> In contrast,
>> a <- tapply(y, list(var1, var2, var3, var4), sum)
>>
>> gives me results for everything including empty subsets, but in an
>> awkward 4-dimensional array that takes me another 10 lines of
>> inefficient code to turn into a 2D data.frame.
>>
>> Is there a way to directly do this calculation INCLUDING results for
>> empty subsets, and still obtain a 2D array, matrix, or data.frame?  OR
>> alternatively is there a simple way to mush the 4D result from the
>> tapply into a 2D matrix/data.frame?
>>
>> thanks very much in advance for any help!
>>
>> -jlb
>>
>> -- 
>> ************************************
>> Joseph P. LeBouton
>> Forest Ecology PhD Candidate
>> Department of Forestry
>> Michigan State University
>> East Lansing, Michigan 48824
>>
>> Office phone: 517-355-7744
>> email: lebouton at msu.edu
>>
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> 
> 

-- 
************************************
Joseph P. LeBouton
Forest Ecology PhD Candidate
Department of Forestry
Michigan State University
East Lansing, Michigan 48824

Office phone: 517-355-7744
email: lebouton at msu.edu