2009/12/17 Joel Fürstenberg-Hägg <joel_furstenberg_h...@hotmail.com>:
>
> Hi all,
>
>
>
> I'm have a matrix (X) with observations as rows and parameters as columns.
> I'm trying to exchange all missing values in a column by the column mean
> using the code below, but so far, nothing happens with the NAs... Can anyone
> see where the problem is?
>
>
>
> N<-nrow(X) # Calculate number of rows = 108
> p<-ncol(X) # Calculate number of columns = 88
>
>
> # Replace by columnwise mean
> for (i in colnames(X)) # Do for all columns in the matrix
> {
> for (j in rownames(X)) # Go through all rows
> {
> if(is.na(X[j,i])) # Search for missing value in the given position
> {
> X[j,i]=mean(X[1:p, i]) # Change missing value to the mean of the
> column
> }
> }
> }
>
mean(anything with an NA in it) == NA. You want mean(X[1:p,i],na.rm=TRUE)
> mean(c(1,2,3,NA,4))
[1] NA
> mean(c(1,2,3,NA,4),na.rm=TRUE)
[1] 2.5
I'll leave it to someone else to show you how to speed this code up by
removing the loops...
Barry
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