In R-2.10.0, the development version, function as.factor() uses 17 digit precision for conversion of numeric values to character type. This is very good for the consistency of the resulting factor, however, i expect that people will complain about, for example, as.factor(0.3) being [1] 0.29999999999999999 Levels: 0.29999999999999999
I suggest to extend the "Warning" section of ?as.factor by the following paragraph. If as.factor() is used for a numeric vector, then the numbers are converted to character strings with 17 digit precision using their machine representation. This guarantees that different numbers are converted to different levels, but may produce unwanted results, if the numbers are expected to have limited number of decimal positions. For example, as.factor(c(0.1, 0.2, 0.3)) produces [1] 0.10000000000000001 0.20000000000000001 0.29999999999999999 Levels: 0.10000000000000001 0.20000000000000001 0.29999999999999999 In order to avoid this, convert the numbers to a character vector using formatC() or a similar function before using as.factor(). Petr. ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
