[R] POSIXct value display incorrect for some values

[David Winsemius]

On Jan 24, 2012, at 4:25 PM, Curt Seeliger wrote:

> Yes, you're right about this being a floating point issue.  I guess I
> wasn't clear enough that this was already understood.  I'd have  
> responded
> earlier the response somehow missed my mailbox.
>
> My question is rather whether there is a work around for correctly
> displaying POSIXct values as character strings without modifying
> print.POSIXct().  I've not been able to hit on one yet, though this  
> seems
> like a very simple problem to get past.

format(as.POSIXct(c('2010-06-03 9:03:58.324',
                     '2010-06-03 9:03:58.325'))+.0002,
                     "%y-%m-%d %H:%M:%OS3" )
[1] "10-06-03 09:03:58.324" "10-06-03 09:03:58.325"

>
> cur
>
>> Jim Holtman wrote, on Thu, 19 Jan 2012 20:51:53
>> This is basically FAQ 7.31. WIth floating point number, you have  
>> about 15
>
>> digits of significance, so if you look at the value:
>>
>>> as.numeric(as.POSIXct('2010-06-03 9:03:58.324'))
>>> [1] 1275581038.3239998817
>>
>> when you get down to the milliseconds, this is about as much  
>> accuracy as
>> you will get based on using POSIXct with dates around this century..
>> ...
>
>> On Thu, Jan 19, 2012 at 3:57 PM, Curt Seeliger
> <Seeliger.Curt_at_epamail.epa.gov> wrote:
>>> First, the reproducable example, showing how converting from  
>>> character
> to
>>> POSIXct to character changes the milliseconds in the first time  
>>> stamp
>>> though not in the second:
>>>
>>> as.POSIXct('2010-06-03 9:03:58.324')
>>> [1] "2010-06-03 09:03:58.323 PDT"
>>>
>>> as.POSIXct('2010-06-03 9:03:58.325')
>>> [1] "2010-06-03 09:03:58.325 PDT"
>>>
>>> This seems to be due to truncation of the numeric value of the POSIX
>>> object during conversion to character:
>>>
>>> as.numeric(as.POSIXct('2010-06-03 9:03:58.324'))
>>> [1] 1275581038.3239998817
>>>
>>> Neither format() nor round() seem to be of assistance here.   
>>> Anyone got
> a
>>> solution?
>>> ...
>>
> -- 
> Curt Seeliger, Data Ranger
> Raytheon Information Services - Contractor to ORD
> seeliger.curt at epa.gov
> 541/754-4638
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT