[R] Retain names in conversion of matrix to vector

[Bill.Venables at csiro.au]

There is a slightly surprising way to do this in one step.  Here's an
example

> tmp <- matrix(1:16, 4, 4)
> dimnames(tmp) <- list(letters[1:4], letters[1:4])
> tmp
  a b  c  d
a 1 5  9 13
b 2 6 10 14
c 3 7 11 15
d 4 8 12 16
> as.data.frame(as.table(tmp))
   Var1 Var2 Freq
1     a    a    1
2     b    a    2
3     c    a    3
4     d    a    4
5     a    b    5
6     b    b    6
7     c    b    7
8     d    b    8
9     a    c    9
10    b    c   10
11    c    c   11
12    d    c   12
13    a    d   13
14    b    d   14
15    c    d   15
16    d    d   16
>  


Bill Venables
CSIRO Laboratories
PO Box 120, Cleveland, 4163
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mailto:Bill.Venables at csiro.au
http://www.cmis.csiro.au/bill.venables/ 

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of philozine
Sent: Friday, 15 June 2007 9:04 AM
To: r-help at stat.math.ethz.ch
Subject: [R] Retain names in conversion of matrix to vector

Hi R-listers,

I'm using R only for a few basic functions but am having difficulty
doing something that *should* be simple. I have an nxn matrix, Q, where
Q[i,j] is a directed value (in this case, oil exports from i to j). Note
that Q[i,j]~=Q[j,i]. I imported column names along with the matrix then
copied them to the rows using rownames(Q) <- colnames(Q). Simple so far.

What I'd like to do now is convert Q for export into a vector of values
with the original row and column names intact. Having one vector each
for row, column, and cell would be ideal, e.g., [1,1] = i's name, [1,2]
= j's name, and [1,3] = Q[i, j]. But just being able to export my matrix
data in vector form with the correct row/col names for each observation
would be sufficient.

Thus far I've tried c(), vector(), and a few others, but can't get the
correct results. They do generate the correct vector of matrix values,
but they do not appear to retain both row and column names. (Or, rather,
I have not discovered how to make them do so.)

To illustrate, my data currently look something like this:

    A    B    C    D
A | 0  |.1 |.4  |.6  |
B |.2 | 0  |.2  |.1  |
C |.5  |.9  | 0  |.9  |
D |.7  | 0  |.3  | 0  |

I would like them to look like this (at least when exported as a .txt
file, if not necessary when displayed within R):

  i   j   Q
| A | A | 0 |
| A | B |.1 |
| A | C |.4 |
| A | D |.6 |
| B | A |.2 |
| B | B | 0 |
| B | C |.2 |
[...] and so on

If anybody knows how to do this, I will be extremely appreciative!

Best regards,


       
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