## making data up
# make matrix with some equal values> mat <- cbind(x=rnorm(10),y=rnorm(10),z=rnorm(10))
> mat[c(8,9),"y"] <- mat[c(1,7),"x"]
> mat
x y z
[1,] 0.26116849 0.5823529 -0.96924020
[2,] -0.21415406 0.1085396 2.00542549
[3,] 0.56890081 -1.2526322 0.08539552
[4,] -1.09096693 -1.9369088 0.03079587
[5,] -1.31749886 -1.1437411 -0.29125624
[6,] -0.45941172 0.2997472 0.10329381
[7,] 0.39586456 -0.2587432 -1.29788184
[8,] -0.05066363 0.2611685 -0.47942195
[9,] -0.87602919 0.3958646 -0.53205231
[10,] 0.30059621 -1.9531231 0.22398194>
## find the index of y which corresponds to equivalent value of
## x and find mean. the following function will give search
## through for each x the matching values of y and return
## the value of x, the index of y, and the mean value> t(apply(mat[,c("x","z")], MARGIN=1, FUN=function(v,w) {
+ yindex <- which(abs(v["x"]-w[,"y"]) <
.Machine$double.eps^0.5)
+ if(length(yindex) > 0) {
+
c(xVal=v["x"],indexOfy=yindex,meanVal=mean(c(v["z"],w[yindex,"z"])))
+ } else {
+ c(xVal=v["x"],indexOfy=NA,meanVal=NA)
+ }
+ },w=mat[,c("y","z")]))
x indexOfy meanVal
[1,] 0.26116849 8 -0.724331
[2,] -0.21415406 NA NA
[3,] 0.56890081 NA NA
[4,] -1.09096693 NA NA
[5,] -1.31749886 NA NA
[6,] -0.45941172 NA NA
[7,] 0.39586456 9 -0.914967
[8,] -0.05066363 NA NA
[9,] -0.87602919 NA NA
[10,] 0.30059621 NA NA
Hope this helps.
--- Felix Wave <felix-wave at vr-web.de> wrote:
> Hello,
> I have got a question.
> I've got a matrix (mail end) with the colnames x, y, z. In this matrix
> are different measurements. x and y are risign coordinates.
>
> My question. Always, if the "x" AND "y" coordinates are
the same, I want to
>
> get the mean of their z values.
>
>
> e.q. "
> x" AND "y" in line1 and line8 are identical:
> 29 4.5 --> mean of 1.505713 and 1.495148
>
>
> Thank's a lot.
> Felix
>
>
>
>
> ###############
> ## My R Code ##
> ###############
> INPUT <- readLines(dat.dat)
> INPUT <- gsub("^ ", "", INPUT)
> INPUT <- t( sapply( strsplit(INPUT, split=" "),
as.numeric ) )
> colnames(INPUT) <- c("x", "y", "z" )
>
>
> # HERE START's my PROBLEM #
> if (duplicated(INPUT[,1] & INPUT[,2] ))
> zMEAN <- mean(INPUT[,3] )
>
> # MATRIX with the mean-z values #
> zMATRIX <- matrix(c(INPUT[,1], INPUT[,2], INPUT[,3] ), ncol=3,
byrow=FALSE)
>
>
>
>
> #############
> ## dat.dat ##
> #############
> 29 4.5 1.505713
> 29 4.6 1.580402
> 29 4.7 1.656875
> 29 4.8 1.735054
> 30 0 0
> 30 0.1 0.00096108
> 30 0.2 0.00323831
> 29 4.5 1.495148
> 29 4.6 1.568961
> 29 4.7 1.644467
> 30 0 0
> 30 0.1 0.00093699
> 30 0.2 0.00319411
> 30 0.3 0.00676619"
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>