Re: [R] Questions about date/time and truncating

From: Jonathan Greenberg <jgreenberg_at_arc.nasa.gov>
Date: Fri 20 Oct 2006 - 22:43:24 GMT


Thanks! Worked like a charm!

hourly_met_data$date <-
as.POSIXct(trunc(as.POSIXct(hourly_met_data$date),"day"))

--j

On 10/20/06 3:31 PM, "jim holtman" <jholtman@gmail.com> wrote:

> trunc returns a type of POSIXlt.  You have to apply 'as.POSIXct' to the
> result.
> 
> On 10/20/06, Jonathan Greenberg <jgreenberg@arc.nasa.gov> wrote:

>> I'm getting a weird behavior using R 2.5.0 for MacOS X -- I have a csv file
>> with a "properly formatted" date/time field, e.g. After reading in the csv
>> to "hourly_met_data", with a "date" field
>>
>> hourly_met_data$date <- as.POSIXct(hourly_met_data$date)
>>
>> works exactly as it is supposed to (e.g. Min/max of that field are
>> calculated correctly). However, when I perform this command to convert a
>> date/time to just a date (e.g. I'm removing the hour portion of the
>> date/time):
>>
>> hourly_met_data$newdate <- trunc(hourly_met_data$date,"day")
>>
>> I get:
>>
>> Error in `$<-.data.frame`(`*tmp*`, "newdate", value = list(sec = 0, min = 0,
>> :
>> replacement has 9 rows, data has 252020
>>
>> If I simply set:
>> newdate <- trunc(hourly_met_data$date,"day")
>> And then print the data (e.g. "newdate"), the output appears to have the
>> right number of entries (252,020):
>>
>> ...
>> [99973] "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05"
>> "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05"
>> "2006-06-05" "2006-06-05"
>> [99985] "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05"
>> "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05" "2006-06-05"
>> "2006-06-06" "2006-06-06"
>> [99997] "2006-06-06" "2006-06-06" "2006-06-06"
>> [ reached getOption("max.print") -- omitted 152021 entries ]]
>>
>> But if I enter:
>>
>> length(newdate)
>> [1] 9
>>
>> hourly_met_data$newdate <- newdate gives me the same error as above.
>>
>> Why is this happening? The output appears to have > 250k entries, why is
>> length returning only 9?
>>
>> --j
>>
>> --
>> Jonathan A. Greenberg, PhD
>> NRC Research Associate
>> NASA Ames Research Center
>> MS 242-4
>> Moffett Field, CA 94035-1000
>> Office: 650-604-5896
>> Cell: 415-794-5043
>> AIM: jgrn307
>> MSN: jgrn307@hotmail.com
>>
>> ______________________________________________
>> R-help@stat.math.ethz.ch mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
-- 
Jonathan A. Greenberg, PhD
NRC Research Associate
NASA Ames Research Center
MS 242-4
Moffett Field, CA 94035-1000
Office: 650-604-5896
Cell: 415-794-5043
AIM: jgrn307
MSN: jgrn307@hotmail.com

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Received on Sat Oct 21 08:46:34 2006

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