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Surprise when mapping matrix to image
2 messages · Glynn, Earl, 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