# [R] Expanding a VCV Matrix

Maithula Chandrashekhar m.chandrashekhar1977 at gmail.com
Thu Apr 21 17:08:43 CEST 2011

```Thanks Uwe for your insight. However this could not solve my problem.
Actually, I meant to define 'Str' in this way:

> mat  <- matrix(c(1,2,0,2,5,0.5,0,0.5,3), 3, 3)
> colnames(mat) <- rownames(mat) <- paste("variable", 1:3, sep="")
> mat
variable1 variable2 variable3
variable1         1       2.0       0.0
variable2         2       5.0       0.5
variable3         0       0.5       3.0
>
> Str<- c(paste("variable", 1:4, sep=""), "variable2"); Str
[1] "variable1" "variable2" "variable3" "variable4" "variable2"

Therefore 'variable2' should appear twice in my modified VCV matrix,
which was not there in your suggestion. Is there any better any on how
can I do that? or it is really imposable to achieve?

Thanks,

2011/4/21 Uwe Ligges <ligges at statistik.tu-dortmund.de>:
>
>
> 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?
>>