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Hi Elham, The error message: Error in if (S == 0) { : missing value where TRUE/FALSE needed means that for at least one S, the value is missing. The best advice I can give you is to load the data frame X1 as in your code above, and try something like: which.na<-function(x) return(which(is.na(x))) sapply(X1,which.na) You will then get a list of the positions of any NA values in X1. Jim On

Hello DearI used modifiedmk package for trend analyses.this is my script ?require(modifiedmk)X1<-read.table("c:/elham/first article/r/Spring_NDVI-1.txt",skip=2,header=FALSE)d=dim(X1) outMK<-matrix(-999,nrow=4,ncol=d[2])for (c in