Re: [R] newbie question: ROW average

From: Rolf Turner <rolf_at_math.unb.ca>
Date: Mon 29 May 2006 - 21:55:50 EST


Dimitris Rizopoulos wrote:

> look at ?rowMeans; you can also use "apply(mat, 1, mean)" but
> rowMeans() is better.

	By my reading of the question, this is not what
	Ezhil wants.  He said:

	``I have a 992 x 74 matrix. I would like to form a new matrix
	  by averaging each 4 rows from the original one.''

	I.e. he wants (I think) the first row of the new matrix
	to be the mean of the first 4 rows of the old one, the
	second row of the new matrix to be the mean of rows 5
	through 8 of the old one, and so on.

	One way this could be done is via

	> m.new <- t(apply(array(t(m.old),dim=c(74,4,992/4)),c(1,3),mean))

			cheers,

				Rolf Turner
				rolf@math.unb.ca

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