[R] `bivariate apply'

[Gabor Grothendieck]

The following:

- uses apply to turn the input matrix, x, into a vector of lists, 
  each of which represents one column
- this vector of lists is replicated two different ways and
- mapply is used on the replicated structures.
- finally, reform the result into a matrix

This solution has the property that it does not deal with indices
at all.

biapply <- function(x,f=cor) {
   k <- NCOL( x )
   x <- apply( x, 2, list )
   ff <- function(x,y) f( unlist(x), unlist(y) )
   matrix( mapply( ff, rep(x,rep(k,k)), rep(x,k) ), k, k )
}

# test
x <- matrix( 1:12, 4, 3 )
biapply( x, crossprod )
biapply( x )

--- 
Date: Tue, 16 Dec 2003 14:13:29 +0100 
From: Vito Muggeo <vito.muggeo at giustizia.it>
To: <r-help at stat.math.ethz.ch> 
Subject: [R] `bivariate apply' 

 
 
dear all,

Given a matrix A, say, I would like to apply a bivariate function to each
combination of its colums. That is if

myfun<-function(x,y)cor(x,y) #computes simple correlation of two vectors x
and y

then the results should be something similar to cor(A).

I tried with mapply, outer,...but without success

Can anybody help me?

many thanks in advance,
vito

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