[R] POSIXct-coerced NA's not considered NA by is.na()

[jim holtman]

I think your first problem is the coersion done by 'c' when you are
mixing objects of various types: you have POSIXct and character.  What
were your expections?

> x <- Sys.time()
> str(x)
 POSIXct[1:1], format: "2012-08-24 13:12:31"
> y <- c(x, 'b')
> str(y)
 POSIXct[1:2], format: "2012-08-24 13:12:31" NA
Warning message:
In as.POSIXlt.POSIXct(x, tz) : NAs introduced by coercion
> dput(y)
structure(c("1345828351.75", "b"), class = c("POSIXct", "POSIXt"
))
>

Look at the 'dput' and see that what it is trying to do is to use the
numeric value changed to a character string as a POSIXct value.  So I
am not surprised by the error since it is probably not what you
wanted.  Did you intend to use 'list' instead of 'c'?

On Fri, Aug 24, 2012 at 9:47 AM, Alexander Shenkin <ashenkin at ufl.edu> wrote:
> Hello folks,
>
> I found a strangeness while experimenting with POSIXct vectors and
> lists.  It seems that coerced NA's aren't "real" NAs, at least as
> considered by is.na()?
>
>> date_vec = c(as.POSIXct(now()), as.POSIXct(now()+1),NA,"b")
>> date_vec
> [1] "2012-08-22 15:00:46 COT" "2012-08-22 15:00:47 COT" NA
>
> [4] NA
> Warning message:
> In as.POSIXlt.POSIXct(x, tz) : NAs introduced by coercion
>> date_vec[4]
> [1] NA
> Warning message:
> In as.POSIXlt.POSIXct(x, tz) : NAs introduced by coercion
>> is.na(date_vec[4])
> [1] FALSE
>> is.na(date_vec[3])
> [1] TRUE
>> is.POSIXct(date_vec[4])
> [1] TRUE
>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.