[R] Surprise when mapping matrix to image
Prof Brian Ripley
ripley at stats.ox.ac.uk
Thu Aug 26 22:43:50 CEST 2004
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
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
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