Howdy,
I'm no plyr master, but here's my 2 cents ...
On Wed, Apr 7, 2010 at 5:15 PM, Stuart Andrews <stu.andr...@gmail.com> wrote:
> Hi,
>
> I am confused by results from:
>
>> ddply(aa, names(aa), colwise(sum))
>
> I thought ddply was just calling colwise(sum)() with each column. However
> ddply() returns a 13 x 5 result !!
>
> The general result I expected is similar to that of apply() , or using
> colwise(sum)() alone. Shouldn't ddply() produce the same ?
Not sure what exactly is happening, but I don't think I'd expect ddply
to produce the same as the example you gave, since the second arg to
ddply determines how the aa data.frame should be split (row-wise)
before the colwise(...) do-hicky is called.
I'm not sure, but what are you trying to get at by row-wise splitting
`aa` by c('a', 'b', 'c', 'd', 'e') [ie. namaes(aa)]?
>
> Thanks in advance for your help,
> - Stuart Andrews
>
>
>> set.seed(1234)
>> aa = as.data.frame(matrix(rnorm(100)>0.3,nrow=20))
>> names(aa) = c('a','b','c','d','e')
>> head(aa)
> a b c d e
> 1 FALSE FALSE FALSE TRUE TRUE
> 2 TRUE TRUE FALSE TRUE FALSE
> 3 TRUE TRUE FALSE TRUE TRUE
> 4 TRUE FALSE FALSE TRUE FALSE
> 5 TRUE FALSE FALSE TRUE FALSE
> 6 FALSE FALSE FALSE FALSE TRUE
>
>> ddply(aa, names(aa), colwise(sum))
> a b c d e
> 1 0 0 0 0 0
> 2 0 0 0 0 2
> 3 0 0 0 4 0
> 4 0 0 0 1 1
> 5 0 0 1 0 0
> 6 0 0 2 0 2
> 7 0 0 1 1 0
> 8 0 2 0 0 0
> 9 0 1 0 0 1
> 10 1 0 0 0 0
> 11 2 0 0 0 2
> 12 1 0 0 1 0
> 13 1 0 0 1 1
>
>> apply(as.matrix(aa),2,sum)
> a b c d e
> 5 3 4 8 9
>
>> colwise(sum)(aa)
> a b c d e
> 1 5 3 4 8 9
>
>
> ... Isn't ddply() just doing something like this for each column??
>
>> colwise(sum)(aa[,1,drop=F])
> a
> 1 5
That's what colwise is doing per each column of the data.frame it's
working on ... ddply does the split-by-row/apply/merge magic on the
data frame and is giving colwise smaller chunks of `aa` to work on at
a time...
So, to summarize, I think you just need to figure out the correct 2nd
arg to ddply for your specific problem.
-steve
--
Steve Lianoglou
Graduate Student: Computational Systems Biology
| Memorial Sloan-Kettering Cancer Center
| Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact
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