Will this do?
library(plyr)
ddply(my_df, .(a), summarize, mm = mean(dat), number = length(dat))
John Kane
Kingston ON Canada
> -----Original Message-----
> From: ashen...@ufl.edu
> Sent: Wed, 20 Mar 2013 14:57:36 -0500
> To: r-help@r-project.org
> Subject: [R] summarize dataframe based on multiple cols, not their
> combinations
>
> Hi folks,
>
> I'm trying to figure out how to get summarized data based on multiple
> columns. However, instead of giving summaries for every combination of
> categorical columns, I want it for each value of each categorical column
> regardless of the other columns. I could do this with three different
> commands, but i'm wondering if there's a more elegant way that I'm
> missing. Thanks!
>
> allie
>
>> my_df = data.frame(a = c(1,1,1,0,0,0), b=c(0,0,0,1,1,1),
> c=c(1,0,1,0,1,0), dat=c(10,11,12,13,14,15))
>
>> my_df
> a b c dat
> 1 1 0 1 10
> 2 1 0 0 11
> 3 1 0 1 12
> 4 0 1 0 13
> 5 0 1 1 14
> 6 0 1 0 15
>
>> # not what I want
>> ddply(my_df, .(a,b,c), function(x) c("mean"=mean(x$dat), "n"=nrow(x)))
> a b c mean n
> 1 0 1 0 14 2
> 2 0 1 1 14 1
> 3 1 0 0 11 1
> 4 1 0 1 11 2
>
> What I want:
> a b c mean n
> 1 1 * * 11 3
> 2 * 1 * 14 3
> 3 * * 1 12 3
>
> where "*" refers to any value of the other columns.
>
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