[R] Inverse function to 'which'?

[Henrik Bengtsson]

Is there an inverse function to 'which' available, which creates a logical
vector/matrix from indices? I wrote my own, but if there is a standard
function I would like to use that instead. Example:

x <- c(TRUE, TRUE, FALSE, TRUE, FALSE, FALSE)
unwhich(which(x))            # [1] TRUE TRUE FALSE TRUE
unwhich(which(x), length(x)) # [1] TRUE TRUE FALSE TRUE FALSE FALSE

y <- matrix(x, nrow=3, ncol=2)
unwhich(which(y, arr.ind=TRUE))          # "Minimum" size
unwhich(which(y, arr.ind=TRUE), dim(y))  # Same dimensions as y

Thanks

Henrik Bengtsson
h e n r i k b @ b r a j u . c o m

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._