[R] matrix to vector

[Peter Dalgaard]

Ian Coe 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. 

 > cbind(expand.grid(rownames(x),colnames(x)),as.vector(x))
   Var1 Var2 as.vector(x)
1    d    a            1
2    e    a            2
3    f    a            3
4    d    b            4
5    e    b            5
6    f    b            6
7    d    c            7
8    e    c            8
9    f    c            9

 > x <- matrix(rnorm(700*700),700)
 > rownames(x) <- paste("R",1:700)
 > colnames(x) <- paste("C",1:700)
 > system.time(foo <- 
cbind(expand.grid(rownames(x),colnames(x)),as.vector(x)))
    user  system elapsed
   1.082   0.107   1.193


>  
> 
> 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     
> 
>  
> 
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> 
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-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
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