Replacing values in data.table by array indexing

[demuellae]

Hi,
I am still new to this great package. So sorry, if this has been answered or addressed before.
I have the following problem:
Let's say, I have a data.table, e.g.

dt <- data.table(letters=letters, random1=rnorm(26), index=1:26)

now, I would like to replace values at specific indices, given in a separate, logical-valued matrix of equal dimension by NA.

maskMatrix <- matrix(sample(c(TRUE,FALSE), nrow(dt)*ncol(dt), replace=TRUE), nrow=nrow(dt), ncol=ncol(dt))

using data.frames I used to be able to do this:

dt[maskMatrix] <- NA

What would be a correct and efficient way to do this with data.table objects?

Thanks for your help!

Best,
demuellae

[demuellae]

To clarify: dt[maskMatrix] <- NA works
However, I read somewhere that you should rather use the := notation to do the replacements in place. I am curious for such a solution.

[MichaelChirico]

for (jj in seq_len(ncol(maskMatrix))) {
  set(DT, maskMatrix[ , jj], jj, NA)
}

PS you're likely to get a much faster response for this type of question on Stack Overflow

[jangorecki]

related to #657