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 <[email protected]> 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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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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David Winsemius, MD
West Hartford, CT
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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