Oh, I should have mentioned that the result of melt is a data.frame, not a
matrix. You can convert with as.matrix if you like.
I should also have shown that dimnames are carried along:
> m <- matrix(1:4,2,2,dimnames=list(x=c('a','b'),y=c('x','y')))
> m
y
x x y
a 1 3
b 2 4
> melt(m)
x y value
1 a x 1
2 b x 2
3 a y 3
4 b y 4
> as.matrix(melt(m))
x y value
[1,] "a" "x" "1"
[2,] "b" "x" "2"
[3,] "a" "y" "3"
[4,] "b" "y" "4"
On Fri, May 29, 2009 at 2:53 PM, Stavros Macrakis <macra...@alum.mit.edu>wrote:
> Not sure what you mean by "permutations" here. I think what you mean is
> that given a matrix m, you want a matrix whose rows are c(i,j,m[i,j]) for
> all i and j. You can use the `melt` function in the `reshape` package for
> this. See below.
>
> Hope this helps,
>
> -s
>
> > library(reshape)
> > melt(matrix(1:4,2,2))
> X1 X2 value
> 1 1 1 1
> 2 2 1 2
> 3 1 2 3
> 4 2 2 4
>
> big <- matrix(1:700^2,700,700)
> > head(melt(big))
> X1 X2 value
> 1 1 1 1
> 2 2 1 2
> 3 3 1 3
> 4 4 1 4
> 5 5 1 5
> 6 6 1 6
> > system.time(melt(big))
> user system elapsed
> 0.08 0.00 0.08
>
>
> On Fri, May 29, 2009 at 2:08 PM, Ian Coe <i...@connectcap.com> wrote:
>
>> Hi,
>>
>> Is there a way to convert a matrix into a vector representing all
>> permutations of values and column/row headings with native R functions?
>> I did this with 2 nested for loops and it took about 25 minutes to run
>> on a ~700x700 matrix. I'm assuming there must be a smarter way to do
>> this with R's vector commands, but being new to R, I'm having trouble
>> making it work.
>>
>>
>>
>> Thanks,
>>
>> Ian
>>
>>
>>
>> [a] [b] [c]
>>
>> [d] 1 4 7
>>
>> [e] 2 5 8
>>
>> [f] 3 6 9
>>
>>
>>
>> a d 1
>>
>> a e 2
>>
>> a f 3
>>
>> b d 4
>>
>> b e 5
>>
>> b f 6
>>
>> c d 7
>>
>> c e 8
>>
>> c f 9
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Ian Coe
>>
>>
>>
>> Connective Capital Management, LLC
>>
>> 385 Homer Ave.
>>
>> Palo Alto, CA 94301
>>
>> (650) 321-4826 ext. 03
>>
>>
>>
>> CONFIDENTIALITY NOTICE: This e-mail communication (inclu...{{dropped:23}}
>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
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