[R] Summarizing counts by multiple factors

[David Winsemius]

On May 11, 2010, at 9:08 PM, David Winsemius wrote:

>
> On May 11, 2010, at 8:38 PM, Noah Silverman wrote:
>
>> Hi,
>>
>> An example data set is:
>>
>> group    level    color
>> A        1        "blue"
>> A        1        "Red"
>> B        1        "blue"
>> B        2        "Red"
>> A        2        "Red"
>> B        2        "Red"
>> B        2        "blue"
>> B        2        "blue"
>> A        2        "blue"
>> A        2        "Red"
>>
>>
>> I'd like to compute a summary of counts for each combination of  
>> group, level, color.
>>
>> An example output would be something like this:
>> group    level    color        count
>> A        1        "blue"        1
>> A        2        "red"        2
>> B        2        "red"        2
>> etc..
>>
>>
>> The tapply function seems to do this for a single variable, but I  
>> can figure out to to do it for combinations of more than one factor.
>
> This doesn't work?
>
> tapply(example$color, c(example$group, example$level), length)

I guess not. so perhaps:

as.data.frame( table(example) )

-- 
David
>
>
>> I also see the ave function, but can't figure out how to apply it  
>> to multiple factors.
>
> It would give you as many lines as in the original which is not what  
> you want.
>
> -- 
> David,
>>
>> Any suggestions?
>>
>> Thanks
>>
>> ______________________________________________
>> R-help at 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.
>
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> R-help at 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.

David Winsemius, MD
West Hartford, CT