[R-sig-eco] Linear Model of Data in Matrix Form

[Ben Bolker]

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On 11-04-02 10:39 PM, Jane Shevtsov wrote:
> I have data in matrix form from a parameter scan of a food web
> simulation. (The matrix entry M[i,j] gives the variable of interest
> for a web size i and connectance j.) How would I find an equation
> expressing the variable of interest to web size and connectance? Can
> lm() do it?
> 
> Thanks,
> Jane Shevtsov
> 

  suppose your size and connectance vectors were sizevec and connvec.
Then something like

dimnames(M) <- list(sizevec,connvec)
library(reshape)
X <- melt(M)
lm(value~X1+X2)

  will do it.
	
  Mini example:

> z <- matrix(1:9,nrow=3,dimnames=list(1:3,4:6))
> library(reshape)
Loading required package: plyr

Attaching package: 'reshape'

The following object(s) are masked from 'package:plyr':

    round_any

> str(melt(z))
'data.frame':	9 obs. of  3 variables:
 $ X1   : int  1 2 3 1 2 3 1 2 3
 $ X2   : int  4 4 4 5 5 5 6 6 6
 $ value: int  1 2 3 4 5 6 7 8 9
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