[R] stack or dissolve matrix without double entries

[jim holtman]

Is this what you want:

> x <- matrix(1:16,4)
> rownames(x) <- colnames(x) <- LETTERS[1:4]
> x
  A B  C  D
A 1 5  9 13
B 2 6 10 14
C 3 7 11 15
D 4 8 12 16
> require(reshape)
> # create single list
> z <- melt(x)
> z
   X1 X2 value
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
> # now extract just the lower matrix
> z[as.vector(lower.tri(x)),]
   X1 X2 value
2   B  A     2
3   C  A     3
4   D  A     4
7   C  B     7
8   D  B     8
12  D  C    12


On Thu, Oct 9, 2008 at 11:31 AM, Marten Winter <marten.winter at ufz.de> wrote:
> Heja,
>
> I've some bigger distance-matrices like this:
>
> num [1:3231, 1:3231] 0.000 0.176 0.176 0.176 0.176 ...
>  - attr(*, "dimnames")=List of 2
>  ..$ : chr [1:3231] "A" "B" "C" "D" ...
>  ..$ : chr [1:3231] A" "B" "C" "D" .
>
> I actually want to convert them into a 2 column dataframe like this:
>
>
> data.frame':   10439361 obs. of  2 variables:
>  $ dist: num  0.000 0.176 0.176 0.176 0.176 ...
>  $ spec: Factor w/  219680 levels "A B",..: 1508 26 27 60 61 62 63 340
> 413 414 ...
>
> preferred appearance:
>
> values                   species
> 1 0.0000000 A A
> 2 0.1761717 A B
> 3 0.1761717 A C
> 4 0.1761717 A D
> 5 0.1761717 A E
>
>
> BUT, I don't need the entries where I have the same distance: "A B" vs.
> "B A", cause the inflate heavily my workspace.
> I know "stack", but I don't know, why but it seems that stack has
> limitations in size (?), it doesn't work.
> I never really understood "reshape".
>
> May someone has a nice way to reshape ;O) a matrix.
>
> THANKS,
> cheers from autumnlike Halle,
> Marten
>
> --
>
> *Marten Winter*
>
> Helmholtz Centre for Environmental Research -- UFZ
> Department of Community Ecology
> Helmholtz-Zentrum für Umweltforschung GmbH - UFZ
> Sektion Biozoenoseforschung
> Theodor-Lieser-Str. 4
> D-06120 Halle (Saale)
> Germany
>
>
> phone: ++49 (0) 345 558-5316 / fax:++49 (0) 345 558-5329
> E-mail: Marten.Winter at ufz.de
> http://www.ufz.de/index.php?en=7081
> DAISIE - Delivering Alien Invasive Species Inventories for Europe
> http://www.europe-aliens.org
>
>
>
>        [[alternative HTML version deleted]]
>
>
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>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?