dat <- data.frame(a=c("","2","3"),b=c("4", NA, "."), c=c(-1,1,3),
d=c(NA,3,2), stringsAsFactors=FALSE)
dat2 <- convertNA(dat, na.character=c("", "."))
dat3 <- convertNA(dat, na.character=".", na.numeric=-1, fromNA=TRUE)
dat
dat2
dat3
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