Applying functions to partitions
Its not clear that the object returned from such an operation would be
a matrix, but if things remain very regular then perhapos you will
succeed with this:
> markmtx <- matrix(scan(textConnection("a a a d g g
+ a a a d g g
+ a a a d g g
+ b b b e h h
+ b b b e h h
+ c c c f i i"), what="character"), nrow=6)
Read 36 items
> nummtx <-matrix(rnorm(36),nrow=6)
> nummtx
[,1] [,2] [,3] [,4] [,5]
[,6]
[1,] -1.49492952 -0.1000962 -0.54546587 -0.536216056 0.1065169
-1.3368842
[2,] -0.64393278 0.3343573 0.76247880 0.282666215 0.2236401
0.8210809
[3,] 1.42879752 -1.3246770 0.06403316 -0.002843621 -0.2990221
-0.4885461
[4,] -0.38740975 0.7800235 0.12819144 0.206188106 0.8481351
0.2572268
[5,] -0.07082702 -0.7870970 0.60560030 -1.381615740 1.4935228
0.1165892
[6,] -0.06916424 -0.5869168 0.39492984 0.016430970 -0.6531722
-0.1194990
> tapply(nummtx, markmtx, FUN=mean)
a b c d
e f g
-0.168826070 -0.037543099 -0.334783145 0.173601720 0.527161589
0.257226798 -0.085579151
h i
-0.131208561 -0.001454904
> matrix(tapply(nummtx, markmtx, FUN=mean), nrow=3)
[,1] [,2] [,3]
[1,] -0.1688261 0.1736017 -0.085579151
[2,] -0.0375431 0.5271616 -0.131208561
[3,] -0.3347831 0.2572268 -0.001454904
David Winsemius On Feb 16, 2009, at 12:43 PM, Titus von der Malsburg wrote: > > Hi list! I have a large matrix which I'd like to partition into > blocks > and for each block I'd like to compute the mean. Following a example > where each letter marks a block of the partition: > > a a a d g g > a a a d g g > a a a d g g > b b b e h h > b b b e h h > c c c f i i > > I'm only interested in the resulting matrix of means. How can this be > done efficiently? > > Thanks! Titus > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.