Try this:
library(doBy)
summaryBy(. ~ day + treat, exampledata, FUN = c(mean, sd))
On Tue, Mar 4, 2008 at 5:24 PM, Levi Waldron <[EMAIL PROTECTED]> wrote:
> I have a dataframe with several different treatment variables, and
> would like to calculate the mean and standard deviation of the
> replicates for each day and treatment variable. It seems like it
> should be easy, but I've only managed to do it for one treatment at a
> time using subset and tapply. Here is an example dataset:
>
> > `exampledata` <-
> structure(list(day = c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L,
> 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L), treat = structure(c(1L, 1L,
> 1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 2L
> ), .Label = c("a", "b"), class = "factor"), replicate = c(1L,
> 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L,
> 3L), height = c(1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.1, 2.2, 2.3,
> 2.4, 2.5, 2.6, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6), weight = c(11.1,
> 11.2, 11.3, 11.4, 11.5, 11.6, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6,
> 13.1, 13.2, 13.3, 13.4, 13.5, 13.6)), .Names = c("day", "treat",
> "replicate", "height", "weight"), class = "data.frame", row.names = c(NA,
> -18L))
>
> > exampledata
> day treat replicate height weight
> 1 1 a 1 1.1 11.1
> 2 1 a 2 1.2 11.2
> 3 1 a 3 1.3 11.3
> 4 1 b 1 1.4 11.4
> 5 1 b 2 1.5 11.5
> 6 1 b 3 1.6 11.6
> 7 2 a 1 2.1 12.1
> 8 2 a 2 2.2 12.2
> 9 2 a 3 2.3 12.3
> 10 2 b 1 2.4 12.4
> 11 2 b 2 2.5 12.5
> 12 2 b 3 2.6 12.6
> 13 3 a 1 3.1 13.1
> 14 3 a 2 3.2 13.2
> 15 3 a 3 3.3 13.3
> 16 3 b 1 3.4 13.4
> 17 3 b 2 3.5 13.5
> 18 3 b 3 3.6 13.6
>
> I would like to combine the replicates and get a dataframe like:
>
> day treat height.mean height.sd weight.mean weight.sd
> 1 a 1.2 0.1 11.2 0.1
> 1 b 1.5 0.1 11.5 0.1
> 2 a 2.2 0.1 12.2 0.1
> 2 b 2.5 0.1 12.5 0.1
> 3 a 3.2 0.1 13.2 0.1
> 3 b 3.5 0.1 13.5 0.1
>
> or two dataframes, one with means and the other with standard deviations.
>
> Thus far I have been doing it a piece at a time, like below (extra
> verbose since tapply doesn't accept the data= argument!), but would
> like to do it for all the measurement columns and all the treatments
> in one go. Thanks!
>
> > tapply(exampledata[exampledata$treat=="a",]$height,exampledata[exampledata$treat=="a",]$day,mean)
> 1 2 3
> 1.2 2.2 3.2
> >
>
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>
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