[R] transform large matrix into list

Stefan Mischke
Tue, 07 Jun 2005 13:28:26 -0000

Ok, ok, I got it! Please don't laugh!
My question is the example from the posting guide! Which even includes
the answer.
How embarrassing...
Stefan




Am 07.06.2005 um 14:55 schrieb Stefan Mischke:

> Dear List
>
> I need to transform a large matrix M with many NAs into a list L with
> one row for each non missing cell. Every row should contain the cell
> value in the first column, and its coordinates of the matrix in column
> 2 and 3.
>
> M:
> 	x1	x2
> y1	1	2
> y2	4	5
> y3	7	8
>
> L:
> v	x	y
> 1	1	1
> 4	1	2
> 7	1	2
> 2	2	1
> 5	2	2
> 8	2	3
>
> I'm trying to do this with a loop, but since my matrix is quite large
> (around 10k^2) this just takes a very long time.
> There must be a more efficient and elegant way to do this. Any hints?