[R] Surprise when mapping matrix to image

[Prof Brian Ripley]

On Thu, 26 Aug 2004, Glynn, Earl wrote:

> Start with:
> 
> > x <- c(1:7,1)
> > dim(x) <- c(2,4)
> > x
>      [,1] [,2] [,3] [,4]
> [1,]    1    3    5    7
> [2,]    2    4    6    1
> 
> 2 Rows of 4 Columns.  Upper-left and lower-right elements of the matrix
> are the same.
> 
> All to this point makes good sense.  

It's pure convention: see below.

> > image(x)
> 
> However, this image shows 2 columns of 4 rows.  The lower-left and
> upper-right elements are the same.   This does not make sense to me.
> Did I miss some simple parameter to "fix" all of this naturally?  Why
> would the numeric matrix of "x" and the image of "x" have such a
> different geometry?

Did you try reading the help for image?  You don't seem to understand it
if you actually did.  It seems you are looking for

	image(t(x)[ncol(x):1, ])

Easy!

Mathematical conventions are just that, conventions.  They differ by field 
of mathematics.  Don't ask us why matrix rows are numbered down but graphs 
are numbered up the y axis, nor why x comes before y but row before 
column.  But the matrix layout has always seemed illogical to me.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595