Check the result of sapply(logical(0), all) ! On 8/12/20, 12:33 PM, "Bioc-devel on behalf of Laurent Gatto" <bioc-devel-boun...@r-project.org on behalf of laurent.ga...@uclouvain.be> wrote:
Dear all, I have a quick question regarding the usage of vapply and sapply. The former is recommended to insure that the output is always a vector of a specific type. For example: > df1 <- data.frame(x = 1:3, y = LETTERS[1:3]) ## OK test > df2 <- data.frame(x = 1:3, y = Sys.time() + 1:3) ## Not OK test > sapply(df1, class) ## vector of chars, OK x y "integer" "character" > sapply(df2, class) ## ouch, not a vector $x [1] "integer" $y [1] "POSIXct" "POSIXt" > vapply(df2, class, character(1)) ## prefer an error rather than a list Error in vapply(df2, class, character(1)) : values must be length 1, but FUN(X[[2]]) result is length 2 There are cases, however, were FUN ensures that the output will be of length 1 and of a expected type. For example - sapply(X, all) - all() always returns logical(1) - sapply(X, length) - always numeric(1) (integer(1) or double(1) for vectors of more than 2^31 - 1 elements) or more generally - sapply(X, slot, "myslot") - slot() will always return a character(1) because @myslot is always character(1) (as defined by the class) Would you still recommend to use vapply() in such cases? Thank you in advance. Laurent _______________________________________________ Bioc-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/bioc-devel _______________________________________________ Bioc-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/bioc-devel