On Wed, Mar 09, 2011 at 02:11:49PM -0500, Simon Urbanek wrote: > match() is a red herring here -- it is really a very specific thing that has > to do with the fact that you're running unique() on a matrix. Also it's much > easier to reproduce: > > > x=c(1,1+0.2e-15) > > x > [1] 1 1 > > sprintf("%a",x) > [1] "0x1p+0" "0x1.0000000000001p+0" > > unique(x) > [1] 1 1 > > sprintf("%a",unique(x)) > [1] "0x1p+0" "0x1.0000000000001p+0" > > unique(matrix(x,2)) > [,1] > [1,] 1 > > and this comes from the fact that unique.matrix uses string representation > since it has to take into account all values of a row/column so it pastes all > values into one string, but for the two numbers that is the same: > > as.character(x) > [1] "1" "1"
I understand the use of match() in the original message by Terry Therneau as an example of a situation, where the behavior of unique.matrix() becomes visible even without looking at the last bits of the numbers. Let me suggest to consider the following example. x <- 1 + c(1.1, 1.3, 1.7, 1.9)*1e-14 a <- cbind(rep(x, each=2), 2) rownames(a) <- 1:nrow(a) The correct set of rows may be obtained using unique(a - 1) [,1] [,2] 1 1.110223e-14 1 3 1.310063e-14 1 5 1.709743e-14 1 7 1.909584e-14 1 However, due to the use of paste(), which uses as.character(), in unique.matrix(), we also have unique(a) [,1] [,2] 1 1 2 5 1 2 Let me suggest to consider a transformation of the numeric columns by rank() before the use of paste(). For example unique.mat <- function(a) { temp <- apply(a, 2, rank, ties.method="max") temp <- apply(temp, 1, function(x) paste(x, collapse = "\r")) a[!duplicated(temp), , drop=FALSE] } unique.mat(a) [,1] [,2] 1 1 2 3 1 2 5 1 2 7 1 2 Petr Savicky. ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel