Seth Falcon wrote: > Uwe Ligges <[EMAIL PROTECTED]> writes: > > >>Charles Dupont wrote: >> >> >>>I was messing around with R and I found an example R behaving oddly: >>> >>>a <- alist(NULL, "bob", c(3,6,2,3)) >>>a >>>a == 'NULL' >>>a == "NULL" >>>a == 'cat' >>> >> >> >>Always use is.null() to test on NULL, as in: > > > What should I do if I want to check for the string "NULL"?
These are all dangerous, hence use the "safe" ways: sapply(a, is.null) sapply(a, identical, "NULL") sapply(a, is.na) sapply(a, identical, "NA") Best, Uwe > >>a <- list(NULL, "NULL", NA, "NA") > > >>a == "NULL" > > [1] TRUE TRUE FALSE FALSE > > >>a == "NA" > > [1] FALSE FALSE TRUE TRUE > > These are because of as.character: > > >>as.character(a) > > [1] "NULL" "NULL" "NA" "NA" > > Yet, > > >>as.character(NULL) > > character(0) > >>as.character(NA) > > [1] NA > > > + seth > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
