# [R] calculate row median of every three columns for a dataframe

Jim Lemon drj|m|emon @end|ng |rom gm@||@com
Fri Apr 17 02:28:15 CEST 2020

```Hi Anna,
I can't think of a simple way, but this function may make you happier:

step_median<-function(x,window) {
x<-unlist(x)
stop<-length(x)-window+1
xout<-NA
nindx<-1
for(i in seq(1,stop,by=window)) {
xout[nindx]<-do.call("median",list(x[i:(i+window-1)]))
nindx<-nindx+1
}
return(xout)
}
apply(df,1,step_median,3)

This should return a matrix where the columns are the medians
calculated from blocks of "window" width on each row of "df". As Bert
noted, you may want to think about a "rolling" median where the
"windows" overlap. This can be done like so:

library(zoo)
apply(df,1,rollmedian,3)

Jim

On Fri, Apr 17, 2020 at 12:32 AM aiguo li via R-help
<r-help using r-project.org> wrote:
>
>  Hi all,
> I need to calculate a row median for every three columns of a dataframe.  I made it work using the following script, but not happy with the script.  Is there a simpler way for doing this?
> df = data.frame("a"=c(2,3,4), "b"=c(3,5,1),"c"=c(1,3,6),"d"=c(7,2,1),"e"=c(2,5,3),"f"=c(4,5,1))tmed <- function(dt) {x = apply(dt,1,median); return(x)}n =seq(1, ncol(df),3)w=0;for (i in n) {   m=i+2;  dt = df[,i:m];   y=tmed(dt);    w = cbind(w,y)}t.med <- w[,2:3]
> Thanks,
> Anna
>
>
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