[R] Expanding a VCV Matrix

[Uwe Ligges]

On 20.04.2011 19:26, Maithula Chandrashekhar wrote:
> 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"



If Str is like the printed one above rather than the code example, you 
can do:

  mat[Str[Str %in% rownames(mat)], Str[Str %in% colnames(mat)]]

Uwe Ligges




> 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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