[R] Expanding a VCV Matrix

From: Maithula Chandrashekhar <m.chandrashekhar1977_at_gmail.com>
Date: Wed, 20 Apr 2011 22:56:33 +0530


Dear all, I have special task to expand a given VCV matrix, however could not accomplice yet. Let say I have following VCV matrix

> mat <- matrix(c(1,2,0,2,5,0.5,0,0.5,3), 3, 3)
> colnames(mat) <- rownames(mat) <- paste("variable", 1:3)
> mat

           variable 1 variable 2 variable 3
variable 1          1        2.0        0.0
variable 2          2        5.0        0.5
variable 3          0        0.5        3.0

Now, say I have a general string vector like this:

> Str <- c(paste("variable", 1:4), "variable2")
> Str

[1] "variable 1" "variable 2" "variable 3" "variable 4" "variable 2"

Now according to this string, I want my previous VCV matrix also expands. Therefore, as "variable 4" is not there in VCV matrix, so it will be ignored. Therefore final VCV matrix will be of order 4, and will look like:

	variable 1	variable 2	variable 3	variable 2
variable 1	1	2	0	2
variable 2	2	5	0.5	5
variable 3	0	0.5	3	0.5
variable 2	2	5	0.5	5

However, I do not think it is just some straightforward expansion, which could be done just by the subsetting mechanism of R. Is there any idea on how can I do it for general case?

Thanks for your time,



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