On Sep 8, 2010, at 11:46 PM, Philippe Grosjean wrote:
On 08/09/10 19:25, David Winsemius wrote:
On Sep 8, 2010, at 1:18 PM, telm8 wrote:
Hi,
I am having some strange problem with detecting "try-error". From
what I
have read so far the following statement:
try( log("a") ) == "try-error"
should yield TRUE, however, it yields FALSE. I can not figure out
why.
Can
someone help?
> class(try( log("a"), silent=TRUE )) == "try-error"
[1] TRUE
This is perfectly correct in this case, but while we are mentioning
a test on the class of an object, the better syntax is:
> inherits(try(log("a)), "try-error")
In a more general context, class may be defined with multiple
strings (R way of subclassing S3 objects). For instance, this does
not work:
> if (class(Sys.time()) == "POSIXct") "ok" else "not ok"
... because the class of a `POSIXct' object is defined as:
c("POSIXt", "POSIXct"). This works:
> if (inherits(Sys.time(), "POSIXct")) "ok" else "not ok"
Alternate valid tests would be (but a little bit less readable):
> if (any(class(Sys.time()) == "POSIXct")) "ok" else "not ok"
or, by installing the "operators" package, a less conventional, but
cleaner code:
> install.packages("operators")
> library(operators)
> if (Sys.time() %of% "POSIXct") "ok" else "not ok"
I have also used if ("try-error" %in% class(try(log("a"))) ) { } else
{ }, but the inherits() form looks at the very least less clunky.
Best,
Philippe Grosjean
Many thanks
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David Winsemius, MD
West Hartford, CT
______________________________________________
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PLEASE do read the posting guide
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______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
