[R] Matrix

[Michael Hannon]

I'm not sure what the OP is looking for in the first two columns, but
he does seem to be looking for only the diagonal and super-diagonal
elements.  Here's some code that makes output that looks similar to
the "Desired output":

mat1 <- matrix(rbind(c(3, 4, 5),
                     c(4, 7, 8),
                     c(5, 8, 9)), nrow=3)
colnames(mat1) <- c('A', 'B', 'C')
rownames(mat1) <- c('A', 'B', 'C')
mat1

col3 <- mat1[row(mat1) >= col(mat1)]
idx12 <- which(row(mat1) >= col(mat1), arr.ind=TRUE)
desiredOutput <- cbind(idx12[ , 2], idx12[ , 1], col3)
desiredOutput

#### If you really want 'A', 'B', 'C'
col1 <- colnames(mat1)[idx12[ , 2]]
col1
col2 <- rownames(mat1)[idx12[ , 1]]
col2

desiredOutput <- cbind(col1, col2, col3)
desiredOutput

-- Mike


On Sat, Jul 16, 2016 at 4:39 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> On 16/07/2016 6:25 PM, Ashta wrote:
>> Hi all,
>>
>> I have a large square matrix (60 x 60)  and found it hard to
>> visualize. Is it possible to change it  as shown below?
>>
>> Sample example (3 x 3)
>>
>>     A   B   C
>> A  3   4   5
>> B  4   7   8
>> C  5   8   9
>>
>> Desired output
>> A A  3
>> A B  4
>> A C  5
>> B B  7
>> B C  8
>> C C  9
>
> Yes, use matrix indexing.  I don't think the 3600 values are going to be
> very easy to read, but here's how to produce them:
>
> m <- matrix(1:3600, 60, 60)
> indices <- expand.grid(row = 1:60, col = 1:60)
> cbind(indices$row, indices$col, m[as.matrix(indices)])
>
> Duncan Murdoch
>
>
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