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

[Alexander Shenkin]

Nice, thanks Ista!

On 3/20/2013 3:18 PM, Ista Zahn wrote:
> 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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