[R] Date/Time to date & time

[Gabor Grothendieck]

On Sun, Sep 20, 2009 at 4:52 PM, Mark Knecht <markknecht at gmail.com> wrote:
> Thanks Gabor,
>   I did try to use dput but it wasn't cooperating and wanted to send
> FAR too much data.

dput(head(x, 10))

>
>   Your method works well for me but as I look at it I don't
> understand the use of double brackets - DF[[1]] - why do you do that?

DF[[1]] is contents of the first column whereas
DF[1] is a data frame with one column -- not the same.

>
>   Anyway, thanks for the fast reponses from you and Jim. Both will
> allow me to make some headway today.
>
> Cheers,
> Mark
>
> On Sun, Sep 20, 2009 at 1:27 PM, Gabor Grothendieck
> <ggrothendieck at gmail.com> wrote:
>> Note that your explanation refers to strptime but the code uses
>> strftime which accounts for the error.
>>
>> Try this:
>>
>>> Lines <- "ENTRY DATE
>> + 3/23/2009 6:30:00 AM
>> + 3/23/2009 6:30:00 AM
>> + 3/23/2009 6:39:00 AM
>> + 3/23/2009 6:39:00 AM
>> + 3/23/2009 6:48:00 AM
>> + 3/23/2009 6:48:00 AM
>> + 3/23/2009 7:00:00 AM"
>>>
>>> DF <- read.csv(textConnection(Lines))
>>> library(chron)
>>> ch <- as.chron(as.character(DF[[1]]), "%m/%d/%Y %I:%M:%S %p")
>>> dd <- dates(ch)
>>> data.frame(Date = dd, Time = times(ch - dd))
>>      Date     Time
>> 1 03/23/09 06:30:00
>> 2 03/23/09 06:30:00
>> 3 03/23/09 06:39:00
>> 4 03/23/09 06:39:00
>> 5 03/23/09 06:48:00
>> 6 03/23/09 06:48:00
>> 7 03/23/09 07:00:00
>>
>> Try using dput next time to facilitate copying of your data into
>> readers' sessions.
>>
>>> dput(DF)
>> structure(list(ENTRY.DATE = structure(c(1L, 1L, 2L, 2L, 3L, 3L,
>> 4L), .Label = c("3/23/2009 6:30:00 AM", "3/23/2009 6:39:00 AM",
>> "3/23/2009 6:48:00 AM", "3/23/2009 7:00:00 AM"), class = "factor")),
>> .Names = "ENTRY.DATE", class = "data.frame", row.names = c(NA,
>> -7L))
>>
>> In the above we used dates and times classes from chron.  as.Date(x) will
>> convert an object to Date class if you want that instead.
>>
>> See R News 4/1 for more on dates and times.
>>
>> On Sun, Sep 20, 2009 at 4:11 PM, Mark Knecht <markknecht at gmail.com> wrote:
>>> Hi,
>>>    Can strptime (or some other function) help me turn the following
>>> column of a data.frame into two new columns, one as date and the other
>>> as time, preserving the AM/PM value?
>>>
>>> Thanks,
>>> Mark
>>>
>>>> B
>>>              ENTRY DATE
>>> 1  3/23/2009 6:30:00 AM
>>> 2  3/23/2009 6:30:00 AM
>>> 3  3/23/2009 6:39:00 AM
>>> 4  3/23/2009 6:39:00 AM
>>> 5  3/23/2009 6:48:00 AM
>>> 6  3/23/2009 6:48:00 AM
>>> 7  3/23/2009 7:00:00 AM
>>>
>>>> strftime(B, tz="", format="%m/%d/%Y %I:%M:%s %p")
>>> Error in as.POSIXlt.default(x, tz = tz) :
>>>  do not know how to convert 'x' to class "POSIXlt"
>>>>
>>>
>>>> strptime(B, format="%m/%d/%Y %I:%M:%s %p")
>>> [1] NA
>>>>
>>>
>>>> mode(B)
>>> [1] "list"
>>>> class(B)
>>> [1] "data.frame"
>>>>
>>>
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>>>
>>
>