[R] block diagonal matrix function

[Gabor Grothendieck]

The zoo package can handle multiway merges of this sort.  The
following example uses your two matrices m1 and m2 but any
number could have been supplied.  Each matrix must be converted
to a zoo object with successive times and then NAs in the result
replaced with zeros.  If the names are important you would have
to set those yourself afterwards:

R> require(zoo)
[1] TRUE
R> m1. <- zoo(m1,1:2)
R> m2. <- zoo(m2,3:5)
R> m. <- merge(m1., m2.)
R> ifelse(is.na(m.),0,m.)
     m1..x m1..y m1..z m2..A m2..B m2..C
[1,]     1     3     3     0     0     0
[2,]     1     1     4     0     0     0
[3,]     0     0     0     2     0     2
[4,]     0     0     0     1     3     2
[5,]     0     0     0     1     2     0


Robin Hankin <rksh <at> soc.soton.ac.uk> writes:

: 
: Hello List
: 
: I have just written a little function that takes two matrices as
: arguments and returns a large matrix that is composed of the two input
: matrices in upper-left position and lower-right position with a padding
: value everywhere else. (function definition and toy example below).  I
: need nonsquare matrices and rowname() and colname() inherited appropriately.
: 
: Two questions:
: 
: (1) Is there a better way to do this? (kronecker() isn't applicable here)
: 
: (2) How do I generalize it to take an arbitrary number of matrices as
:      inputs?
: 
: TIV
: 
: Robin
: 
: 
: "blockdiag" <-
: function (m1, m2, p.tr = 0, p.ll = 0)
: {
:      ## p.tr and p.ll are padding values
:      topleft <- m1
:      topright <- matrix(p.tr, nrow(m1), ncol(m2))
:      colnames(topright) <- colnames(m2)
:      lowleft <- matrix(p.ll, nrow(m2), ncol(m1))
:      lowright <- m2
:      rbind(cbind(topleft, topright), cbind(lowleft, lowright))
: }
: 
: m1 <-
: structure(c(1, 1, 3, 1, 3, 4), .Dim = as.integer(c(2, 3)), .Dimnames = list(
:      c("a", "b"), c("x", "y", "z")))
: 
: m2 <-
: structure(c(2, 1, 1, 0, 3, 2, 2, 2, 0), .Dim = as.integer(c(3,
: 3)), .Dimnames = list(c("I", "II", "III"), c("A", "B", "C")))
: 
: R> m1
:    x y z
: a 1 3 3
: b 1 1 4
: 
: R> m2
:      A B C
: I   2 0 2
: II  1 3 2
: III 1 2 0
: 
: R> blockdiag(m1,m2)
:      x y z A B C
: a   1 3 3 0 0 0
: b   1 1 4 0 0 0
: I   0 0 0 2 0 2
: II  0 0 0 1 3 2
: III 0 0 0 1 2 0
: R>