[R] Repeating grey scale in graph?

[Duncan Murdoch]

On Wed, 16 Feb 2005 15:44:00 +0200, Sander Oom
<slist at oomvanlieshout.net> wrote :

>Thanks Peter!
>
>Of course I only have (nx-1)(ny-1) facets in a x*y plot!
>
>The help page line:
>...
>col 	the color(s) of the surface facets. Transparent colours are 
>ignored. This is recycled to the (nx-1)(ny-1) facets.
>...
>just did not ring a bell.
>
>In fact, it is still not clear to me why it recycles the ramp even 
>though it has a surplus of colours (grey levels)! Why not just ignore 
>the surplus colours?

Your z array is 6 by 7.  Your cols will be mapped to a 5 by 6 array.
They don't look like an array, because the grey() function stripped
off the dimension attribute.

The problem is that if you pass the entries from a 6 by 7 array to
something that expects the entries from a 5 by 6 array, you get things
in the wrong order.   You see the same effect here:

> rownum <- as.vector(row(matrix(NA, 6, 7)))
> matrix(rownum, 6, 7)
     [,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,]    1    1    1    1    1    1    1
[2,]    2    2    2    2    2    2    2
[3,]    3    3    3    3    3    3    3
[4,]    4    4    4    4    4    4    4
[5,]    5    5    5    5    5    5    5
[6,]    6    6    6    6    6    6    6
> matrix(rownum, 5, 6)
     [,1] [,2] [,3] [,4] [,5] [,6]
[1,]    1    6    5    4    3    2
[2,]    2    1    6    5    4    3
[3,]    3    2    1    6    5    4
[4,]    4    3    2    1    6    5
[5,]    5    4    3    2    1    6
Warning message:
data length [42] is not a sub-multiple or multiple of the number of
rows [5] in matrix 

except that in this case you get a warning about the wrong length;
persp doesn't give you the warning.  Maybe it should?

Duncan Murdoch