[R] Any way to apply TWO functions with tapply()?

[David Winsemius]

That was a superb answer to a question that has already appeared in  
various forms on r-help at least 4 times that I can remember just this  
week. I think your text could be appended without much editing into  
the FAQ.  It could then have its own hyperlink, and you wouldn't need  
to type it again the next umpteen times that it will re-appear.

-- 
David.


On May 7, 2010, at 8:50 AM, Gabor Grothendieck wrote:

> tapply does handle functions with vector outputs, e.g. using the built
> in CO2 data set the following data frame is returned:
>
>> f <- function(x) data.frame(mean = mean(x), sd = sd(x))
>> do.call(rbind, tapply(CO2$uptake, CO2$Type, f))
>            mean   sd
> Quebec      33.5 9.67
> Mississippi 20.9 7.82
>
> Note that if you replace data.frame with c in f then you get a matrix
> out instead of a data.frame.
>
> There is also somewhat similar functionality in summaryBy (doBy
> package), summary.formula (Hmisc package), ddply (plyr package), remix
> (remix package), melt and cast (reshape package) and sqldf (sqldf
> package).
>
> Of these summaryBy in the doBy package is particularly easy to specify
> and produces a data frame:
>
> library(doBy)
> summaryBy(uptake ~ Type, data = CO2, FUN = c(mean, sd))
>
> remix and summary.formula in Hmisc have particularly attractive output
> but do not produce data frames.  Hmisc even has a plot method.  The
> specification to remix is also simple here and, in fact, is identical
> to the summaryBy line above except it uses lower case fun.  sqldf uses
> SQL for the specification which may be an advantage if you know SQL
> better than R.
>
> On Fri, May 7, 2010 at 5:39 AM, Phil Wieland <phwiel at gmx.de> wrote:
>>
>> I need to compute the mean and the standard deviation of a data set  
>> and would
>> like to have the results in one table/data frame. I call tapply()  
>> two times
>> and do then merge the resulting tables to have them all in one  
>> table. Is
>> there any way to tell tapply() to use the functions mean and sd  
>> within one
>> function call? Something like tapply(data$response, list(data 
>> $targets,
>> data$conditions), c(mean, sd)).
>>
>> Thanks in advance.
>> --
>> View this message in context: http://r.789695.n4.nabble.com/Any-way-to-apply-TWO-functions-with-tapply-tp2133924p2133924.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
>> ______________________________________________
>> 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.
>>
>
> ______________________________________________
> 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