[R] summarize dataframe based on multiple cols, not their combinations

[Ista Zahn]

How about

library(reshape2)
mdf.m <- melt(my_df, measure.vars=c("a", "b", "c"))
mdf.m <- mdf.m[mdf.m$value > 0, ]

ddply(mdf.m, "variable", function(x) c("mean"=mean(x$dat), "n"=nrow(x)))

?

Best,
Ista

On Wed, Mar 20, 2013 at 3:57 PM, Alexander Shenkin <ashenkin at ufl.edu> wrote:
> 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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