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

Gabor Grothendieck ggrothendieck at gmail.com
Fri May 7 14:50:18 CEST 2010

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

Of these summaryBy in the doBy package is particularly easy to specify
and produces a data frame:

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.
> --
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