POSIXct-coerced NA's not considered NA by is.na()
Thanks for your reply, Jim.
On 8/24/2012 12:14 PM, jim holtman wrote:
I think your first problem is the coersion done by 'c' when you are mixing objects of various types: you have POSIXct and character.
Yes, that's something I may have confounded. Still, the warning I'm getting is "In as.POSIXlt.POSIXct(x, tz) : NAs introduced by coercion". I'm not sure how c()'s coercion works - the warning seems to indicate that c() is finding as.POSIXct. That's strange though, since I would expect to get an error in that case, not just a warning:
as.POSIXct("b")
Error in as.POSIXlt.character(x, tz, ...) : character string is not in a standard unambiguous format
What were your expections?
I was expecting that the NA resulting from the coercion would result in a TRUE value when being operated on by is.na(). Instead, I got:
is.na(date_vec[4])
[1] FALSE
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'?
I'm a bit confused about how you get that from dput. Here's what I see:
dput(date_vec)
structure(c("1345831833", "1345831834", NA, "b"), class = c("POSIXct",
"POSIXt"))
Regardless, I do get the same strange is.na() behavior from the following:
bad_date = "b" class(bad_date) = "POSIXct" bad_date
[1] NA Warning message: In as.POSIXlt.POSIXct(x, tz) : NAs introduced by coercion
is.na(bad_date) # shouldn't this be TRUE?
[1] FALSE As nasty as it may be, shouldn't something showing up as "NA" result in TRUE when being tested by is.na()? Just to put some context around this, I was investigating this issue as I was thinking about converting dataframe columns to dates, and detecting errors in that conversion. thanks, Allie
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