[R] Merging Matrices

[Steven McKinney]

________________________________________
> From: r-help-bounces at r-project.org [r-help-bounces at r-project.org] On Behalf Of duncandonutz [dwadswor at unm.edu]
> Sent: March 19, 2010 1:11 PM
> To: r-help at r-project.org
> Subject: [R] Merging Matrices
> 
> I have two symmetric matrices, but of different dimensions.  The entries are
> identified by specific labels some of which are shared by both matrices.  I
> would like to sum the two matrices, but retain the union of the two.  In
> other words, I want the result to be the same size as the larger of the two
> matrices, but with the entries that they share added together.
> 
> cbind() and rbind() don't work since the matrices are different sizes
> (symmetrically).  Merge doesn't want to cooperate, although it might be
> because I can't understand the documentation. I tried the package "reshape"
> but didn't get very far with that either.  I tried simply adding (+) them,
> but that was a stupid first try.

With appropriate indexing of the matrices via their shared names, 
it can be done as follows:

> A <- matrix(1:9, nrow = 3)
> A[lower.tri(A)] <- A[upper.tri(A)]
> B <- matrix(1:25, nrow = 5)
> B[lower.tri(B)] <- B[upper.tri(B)]
> dimnames(A) <- list(letters[c(2, 4, 5)], letters[c(2, 4, 5)])
> dimnames(B) <- list(letters[1:5], letters[1:5])
> A
  b d e
b 1 4 7
d 4 5 8
e 7 8 9
> B
   a  b  c  d  e
a  1  6 11 16 21
b  6  7 12 17 22
c 11 17 13 18 23
d 12 18 22 19 24
e 16 21 23 24 25
> B[dimnames(A)[[1]], dimnames(A)[[1]]]
   b  d  e
b  7 17 22
d 18 19 24
e 21 24 25
> C <- B
> C[dimnames(A)[[1]], dimnames(A)[[1]]] <- A + B[dimnames(A)[[1]], dimnames(A)[[1]]]
> C
   a  b  c  d  e
a  1  6 11 16 21
b  6  8 12 21 29
c 11 17 13 18 23
d 12 22 22 24 32
e 16 28 23 32 34
> C - B
  a b c d e
a 0 0 0 0 0
b 0 1 0 4 7
c 0 0 0 0 0
d 0 4 0 5 8
e 0 7 0 8 9
> 


HTH

Steve McKinney

> Any help is appreciated!
> --
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