[R] Using dcast with multiple functions to aggregate

[Ista Zahn]

Hi Jokel,

On Thu, Apr 12, 2012 at 7:57 AM, Jokel Meyer <jokel.meyer at googlemail.com> wrote:
> Dear R communitiy,
>
> I am trying to use multiple functions for aggregation within a function
> call for dcast. However this seems to result in an error. Also I have not
> managed to make dcast() work with fun.aggregate=sd. Please find attached
> some example code using the ChickWeight data.
>
> Many thanks for your help!
> Jokel
>
>
> #Chick weight example
>
> names(ChickWeight) <- tolower(names(ChickWeight))
>
>
> sd(ChickWeight$weight) # works fine
>
> mean(ChickWeight$weight) # works fine
>
> length(ChickWeight$weight) # works fine
>
>
> chick_m <- melt(ChickWeight, id=2:4, na.rm=TRUE)

This doesn't do anything interesting, because there is only one measure.var!

>
> dcast(chick_m, time~variable, mean) # works fine
>
> dcast(chick_m, time~variable, length) # works fine
>
>
> dcast(chick_m, time~variable, fun.aggregate=sd) # gives an error

Works on my machine. See session info below.

>
> dcast(chick_m, time~variable, c(mean, length)) # gives an error

?dcast tells you that fun.aggregate must return a single summary
statistic. dcast is not the right function for the job.


For reference, here is my session info:

R version 2.14.2 (2012-02-29)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] C

attached base packages:
[1] splines   stats     graphics  grDevices utils     datasets  methods
[8] base

other attached packages:
[1] plyr_1.7.1       reshape2_1.2.1   foreign_0.8-49   eha_2.0-7
[5] survival_2.36-12

loaded via a namespace (and not attached):
[1] compiler_2.14.2 stringr_0.6     tcltk_2.14.2    tools_2.14.2

Best,
Ista
>
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