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The inverse function to which creates a logical vector/matrix from indices.

which

Unwhich(idx, n = max(idx), useNames = TRUE)

a logical vector of the length n, with TRUE on the positions i.

TRUE

i

the indices as returned by which.

integer, the length of the original vector. This must not be less than max(idx), which is also the default.

max(idx)

logical, determining if the names of the indices should be preserved.

Nick Sabbe

https://stackoverflow.com/questions/7659833/inverse-of-which

ll <- c(TRUE, FALSE, TRUE, NA, FALSE, FALSE, TRUE) names(ll) <- letters[seq(ll)] i <- which(ll) # back again (loosing the names of the FALSEs) Unwhich(i, length(ll))

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