in R, why does as.Date(Inf) display as NA, yet fails the test for being NA-CodePudding

An alternative title to this question is:
When is an NA date not an NA?
Answer: when it is infinity formatted as a date.

Converting infinity to a date results in NA being displayed, but it is not!

> BadDates <- as.Date(c(NA,Inf,-Inf))
> BadDates
[1] NA NA NA
> is.na(BadDates)
[1]  TRUE FALSE FALSE

This causes confusion when trying to catch errors. A work-around is to test for infinity and NA

> is.na(BadDates) & is.infinite(BadDates)
[1] FALSE FALSE FALSE

Is there a better way to manage this quirk of the Date class?

CodePudding user response：

is.finite(as.Date(NA)) and is.infinite(as.Date(NA)) are both FALSE so is.finite will be FALSE for all the bad dates but TRUE for a good date.

BadDates <- as.Date(c(NA,Inf,-Inf))
is.finite(BadDates)
## [1] FALSE FALSE FALSE
 
GoodDate <- Sys.Date()
is.finite(GoodDate)
## [1] TRUE

It works the same without dates so it is not specific to Date class.

x <- c(NA, Inf, -Inf)
is.finite(x)
## [1] FALSE FALSE FALSE

is.finite(3)
## [1] TRUE