calculate row median of every three columns for a dataframe

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

 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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