# [R] Get the difference of values to their own median value

Felix Wave felix-wave at vr-web.de
Wed May 2 09:44:16 CEST 2007

```Hello,
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.

With the following line I got the median value of z for all "x" AND "y" witch
are the same (not every measurment in my list hast the same number of
"x" and "y" values. Sometimes lines are missing.
>MEDIAN  <- na.omit( aggregate(INPUT[,3], by=list(INPUT[,2],INPUT[,1] ), FUN=median ) )

To see the failin of my measurments I want to get the difference between
every measurment and the detected median values.
The aim would be to have a list with different colums (for every measurment)
with the difference between measurment 1,2,3, ..., x and the median.

Has anybody an idea?

I though I could split the measurment list. The beginning of every measurment
can be found with
>START     <- grep(" 0 0.0 0.00000000", INPUT)
But not every measurment has the same length and I don't have always the
same number of measurments.

I hope you can help me.

Thank's a lot.
Felix

###############
## My R Code ##
###############
INPUT           <- gsub("^ ", "", INPUT)
INPUT           <- t( sapply( strsplit(INPUT, split=" "), as.numeric ) )
colnames(INPUT) <- c("x", "y", "z" )

#############
## 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"

```