R help - Jul 2012 - Possible bug in class 'POSIXlt' when including microseconds?

Dear list,

I'm a bit puzzled by an ambiguity with respect to the representation of 
micro-/milliseconds when using 'POSIXlt' objects.

It seems that the last digit of  the 'sec' attribute sometimes seems to 
differ from the digits shown when printing the 'POSIXlt' object.
You'll
find a little SO post with some example code here: 
http://stackoverflow.com/questions/11725517/ambiguity-with-posixlt-representation-when-microseconds-are-included.

In case you don't want to have a look at that, here's another short
example:

|opts<-  options(digits.secs=6)
x<-  "2012-07-30 12:10:09.123123"

posix<-  as.POSIXlt(x,  tz="Europe/Berlin")
>  posix
[1]  "2012-07-30 12:10:09.123122 Europe/Berlin"
>  posix$sec
[1]  9.123123
|

# Manually changing the 'sec' attribute

|posix$sec<-  9.123122
>  posix
[1]  "2012-07-30 12:10:09.123122 Europe/Berlin"
# Still '.123122'

posix$sec<-  9.123124
>  posix
[1]  "2012-07-30 12:10:09.123124 Europe/Berlin"
# Now it's '.123124' in both 'representations'
|


Thanks a lot for any clarification on this!
Janko

	[[alternative HTML version deleted]]

FAQ 7.31

In floating point, you get about 15 digits of precision.  If you look
at the value of time for today you will see:

1343668783

If you add 5 more digits after the decimal point, you will see that
there is not resolution to a microsecond level.  I usually assume that
I can get millisecond resolution from POSIXct values.

On Mon, Jul 30, 2012 at 12:52 PM, Janko Thyson
<janko.thyson.rstuff at googlemail.com> wrote:
> Dear list,
>
> I'm a bit puzzled by an ambiguity with respect to the representation of
> micro-/milliseconds when using 'POSIXlt' objects.
>
> It seems that the last digit of  the 'sec' attribute sometimes
seems to
> differ from the digits shown when printing the 'POSIXlt' object.
You'll
> find a little SO post with some example code here:
>
http://stackoverflow.com/questions/11725517/ambiguity-with-posixlt-representation-when-microseconds-are-included.
>
> In case you don't want to have a look at that, here's another short
example:
>
> |opts<-  options(digits.secs=6)
> x<-  "2012-07-30 12:10:09.123123"
>
> posix<-  as.POSIXlt(x,  tz="Europe/Berlin")
>
>>  posix
> [1]  "2012-07-30 12:10:09.123122 Europe/Berlin"
>
>>  posix$sec
> [1]  9.123123
> |
>
> # Manually changing the 'sec' attribute
>
> |posix$sec<-  9.123122
>>  posix
> [1]  "2012-07-30 12:10:09.123122 Europe/Berlin"
> # Still '.123122'
>
> posix$sec<-  9.123124
>>  posix
> [1]  "2012-07-30 12:10:09.123124 Europe/Berlin"
> # Now it's '.123124' in both 'representations'
> |
>
>
> Thanks a lot for any clarification on this!
> Janko
>
>         [[alternative HTML version deleted]]
>
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-- 
Jim Holtman
Data Munger Guru

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