[R] Date Time in R

William Dunlap wdunlap at tibco.com
Tue Jul 26 18:49:20 CEST 2016 

Can you show us what transformations you tried when
you saw the column called 'date' was a factor?

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, Jul 26, 2016 at 9:33 AM, Shivi Bhatia <shivipmp82 at gmail.com> wrote:

> Thanks Tom for the recommendation. This is now working.
>
> Apologies if this sounds like a juvenile but i am not very good with dates
> in R. What i initially did when i saw date as factor and then tried
> converting with lot many transformation that is where it went bad.
>
> But thanks to all this is really what i wanted.
>
> On Tue, Jul 26, 2016 at 9:58 PM, Tom Wright <tom at maladmin.com> wrote:
>
> > So this looks correct so far.
> >
> >
> >
> > # convert strings (or factors) to a date object
> >
> > a1$date <- as.Date(a1$date, “%m-%d-%y”)
> >
> >
> >
> > # Note the date object is now displayed in the format %Y-%m-%d by default
> >
> > # so no need for the mdy() or ymd() function
> >
> >
> >
> > # extract the weekdays as number
> >
> > weekdays <- wday(a1$date)
> >
> >
> >
> > # note can’t have spaces in variable names
> >
> > week_names <- wday(a1$date, label=TRUE)
> >
> >
> >
> >
> >
> > *From:* Shivi Bhatia [mailto:shivipmp82 at gmail.com]
> > *Sent:* July 26, 2016 12:16 PM
> > *To:* Tom Wright <tom at maladmin.com>
> > *Cc:* David L Carlson <dcarlson at tamu.edu>; r-help <r-help at r-project.org>
> >
> > *Subject:* Re: [R] Date Time in R
> >
> >
> >
> > Hello Tom,
> >
> >
> >
> > Please find the details: (i have changed name from eir to a1, rest all is
> > same)
> >
> >
> >
> > str(a1$date)
> >
> >  Factor w/ 32 levels "05-30-16","05-31-16",..: 1 1 1
> >
> >
> >
> > head(a1$date)
> >
> > 05-30-16 05-30-16 05-30-16 05-30-16 05-30-16 05-30-16
> >
> > 32 Levels: 05-30-16 05-31-16 06-01-16 06-02-16 06-03-16 06-04-16 06-05-16
> > 06-06-16 06-07-16 06-08-16
> >
> >
> >
> > Thanks again!!!
> >
> >
> >
> > On Tue, Jul 26, 2016 at 9:38 PM, Tom Wright <tom at maladmin.com> wrote:
> >
> > Hi again Shiva,
> > I think what we need to see is the output from:
> >
> > str(eid$date)
> >
> > and perhaps
> > head(eid$date)
> >
> > If you can send this information before doing any processing on the date
> > (i.e. before the as.Date() function) we may be able to help.
> >
> >
> >
> > -----Original Message-----
> > From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Shivi
> > Bhatia
> > Sent: July 26, 2016 11:46 AM
> > To: David L Carlson <dcarlson at tamu.edu>
> > Cc: r-help <r-help at r-project.org>
> > Subject: Re: [R] Date Time in R
> >
> > Hi David please see the code and some reproducible data:
> > eir$date<- as.Date(eir$date,format = "%m-%d-%y")  then i had used the
> > lubridate library to help with the dates:
> > install.packages("lubridate")
> > library(lubridate)
> > eir$date <- mdy(eir$date)
> > weekdays <- wdy(eir$date)
> > week names <- wdy(eir$date, label = TRUE)
> >
> > This the output from the file:
> >
> > structure(list(date = structure(c(NA_real_, NA_real_, NA_real_), class =
> > "Date"),
> >
> > month = structure(c(2L, 2L, 2L), .Label = c("Jun","May"), class =
> > "factor"),
> >
> > day = c(30L, 30L, 30L),
> >
> > weekday = structure(c(2L,2L, 2L), .Label = c("Fri", "Mon", "Sat", "Sun",
> > "Thu", "Tue","Wed"), class = "factor"),
> >
> > survey_rating = c(3L, 2L, 3L), query_status = c("Yes", "Don't
> know","No"),
> >
> >  a = c("05-30-16", "05-30-16", "05-30-16")), .Names = c("date","month",
> > "day", "weekday", "survey_rating"), row.names = c(NA, 3L), class =
> > "data.frame")
> >
> > There are several other variables that i have removed which are not
> > relevant
> > in this context.
> >
> > On Tue, Jul 26, 2016 at 8:55 PM, David L Carlson <dcarlson at tamu.edu>
> > wrote:
> >
> > > Show us the output, don’t just tell us what you are seeing. If the
> > > dates are correct in the csv file, show us the structure of the data
> > > frame you created with read.csv() and show the command(s) you used to
> > > convert the character data to date format. The solution is likely to
> > > be simple if you will cut/paste the R console and not just describe
> what
> > > is happening.
> > >
> > >
> > >
> > > David C
> > >
> > >
> > >
> >
> > > *From:* Shivi Bhatia [mailto:shivipmp82 at gmail.com]
> > > *Sent:* Tuesday, July 26, 2016 10:08 AM
> > > *To:* David L Carlson
> > >
> > > *Subject:* Re: [R] Date Time in R
> >
> > >
> > >
> > >
> > > Hi David,
> > >
> > > This gives the results accurately. The first line shows all the
> > > variable names and the rest shows all values stored for each of the
> > > variable. Here date is appearing as correct.
> > >
> > >
> > >
> > > Thanks, Shivi
> > >
> > >
> > >
> > > On Tue, Jul 26, 2016 at 7:39 PM, David L Carlson <dcarlson at tamu.edu>
> > > wrote:
> > >
> > > What does this produce?
> > >
> > > > readLines("YourCSVfilename.csv", n=5)
> > >
> > > If the data are in Excel, the date format used in .csv files is not
> > > always in the same as the format used when viewing dates in the
> > > spreadsheet.
> > >
> > > -------------------------------------
> > > David L Carlson
> > > Department of Anthropology
> > > Texas A&M University
> > > College Station, TX 77840-4352
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Shivi
> > > Bhatia
> > > Sent: Tuesday, July 26, 2016 7:42 AM
> > > To: Marc Schwartz
> > > Cc: R-help
> > > Subject: Re: [R] Date Time in R
> > >
> > > Thanks Marc for the help. this really helps.
> > > I think there is some issue with the data saved in csv format for this
> > > variable as when i checked:
> > > str(eir$date)- this results in :-
> > > Date[1:5327], format: NA NA NA NA NA.
> > >
> > > Thanks again.
> > >
> > > On Tue, Jul 26, 2016 at 5:58 PM, Marc Schwartz <marc_schwartz at me.com>
> > > wrote:
> > >
> > > > Hi,
> > > >
> > > > That eir$date might be a factor is irrelevant. There is an as.Date()
> > > > method for factors, which does the factor to character coercion
> > > internally
> > > > and then calls as.Date.character() on the result.
> > > >
> > > > Using the example data below:
> > > >
> > > > eir <- data.frame(date = c("05-30-16", "05-30-16", "05-30-16",
> > > >                            "05-30-16", "05-30-16", "05-30-16"))
> > > >
> > > > > str(eir)
> > > > 'data.frame':   6 obs. of  1 variable:
> > > >  $ date: Factor w/ 1 level "05-30-16": 1 1 1 1 1 1
> > > >
> > > > > eir
> > > >       date
> > > > 1 05-30-16
> > > > 2 05-30-16
> > > > 3 05-30-16
> > > > 4 05-30-16
> > > > 5 05-30-16
> > > > 6 05-30-16
> > > >
> > > > eir$date <- as.Date(eir$date, format = "%m-%d-%y")
> > > >
> > > > > str(eir)
> > > > 'data.frame':   6 obs. of  1 variable:
> > > >  $ date: Date, format: "2016-05-30" ...
> > > >
> > > > > eir
> > > >         date
> > > > 1 2016-05-30
> > > > 2 2016-05-30
> > > > 3 2016-05-30
> > > > 4 2016-05-30
> > > > 5 2016-05-30
> > > > 6 2016-05-30
> > > >
> > > > eir$days <- weekdays(eir$date)
> > > >
> > > > > str(eir)
> > > > 'data.frame':   6 obs. of  2 variables:
> > > >  $ date: Date, format: "2016-05-30" ...
> > > >  $ days: chr  "Monday" "Monday" "Monday" "Monday" ...
> > > >
> > > > > eir
> > > >         date   days
> > > > 1 2016-05-30 Monday
> > > > 2 2016-05-30 Monday
> > > > 3 2016-05-30 Monday
> > > > 4 2016-05-30 Monday
> > > > 5 2016-05-30 Monday
> > > > 6 2016-05-30 Monday
> > > >
> > > >
> > > > I would check to be sure that you do not have any typos in your code.
> > > >
> > > > Regards,
> > > >
> > > > Marc Schwartz
> > > >
> > > >
> > > > > On Jul 26, 2016, at 6:58 AM, Shivi Bhatia <shivipmp82 at gmail.com>
> > > wrote:
> > > > >
> > > > > Hello Again,
> > > > >
> > > > > While i tried your solution as you suggested above it seems to be
> > > > working.
> > > > > Here is the output
> > > > > temp<- dput(head(eir$date))
> > > > > c("05-30-16", "05-30-16", "05-30-16", "05-30-16", "05-30-16",
> > > "05-30-16")
> > > > > however it still shows class(eir$date) as character and hence i
> > > > > cannot
> > > > find
> > > > > weekdays from this variable.
> > > > >
> > > > > Sorry but i still dont understand in totality how R reads dates
> > > > > even
> > > > though
> > > > > have tried enough.
> > > > >
> > > > > Regards, Shivi
> > > > >
> > > > >
> > > > > On Tue, Jul 26, 2016 at 5:12 PM, Shivi Bhatia
> > > > > <shivipmp82 at gmail.com>
> > > > wrote:
> > > > >
> > > > >> Thanks Duncan for the quick response. I will check again as you
> > > > suggested.
> > > > >> If that doesn't work i will share a reproducible example.
> > > > >>
> > > > >> Thanks again!!!!
> > > > >>
> > > > >> On Tue, Jul 26, 2016 at 4:43 PM, Duncan Murdoch <
> > > > murdoch.duncan at gmail.com>
> > > > >> wrote:
> > > > >>
> > > > >>> On 26/07/2016 7:05 AM, Shivi Bhatia wrote:
> > > > >>>
> > > > >>>> Hi Team,
> > > > >>>>
> > > > >>>> This scenario may have come across a number of times however i
> > > checked
> > > > >>>> nabble & SO and couldn't find a solution hence request
> assistance.
> > > > >>>>
> > > > >>>> I have a date variable in my data-set eir. The class of this
> > > > >>>> var was character while i had read the file in r studio.
> > > > >>>> Example of date -
> > > > >>>> 05-30-16
> > > > >>>>
> > > > >>>> To change this i have used eir$date<- as.Date(eir$date,
> > > > >>>> "%m-%d-%y").
> > > > This
> > > > >>>> converts it to a date variable. However when i check few obs
> > > > >>>> with head(eir$date) all the results are <NA>.
> > > > >>>>
> > > > >>>
> > > > >>> I think you don't have character data like that, because I see
> > > > >>>
> > > > >>>> as.Date("05-30-16", "%m-%d-%y")
> > > > >>> [1] "2016-05-30"
> > > > >>>
> > > > >>> I'd guess eir$date is really a factor, because character data is
> > > > >>> frequently changed to factor automatically.  If that's the case,
> > > > >>> this should work for the conversion:
> > > > >>>
> > > > >>> as.Date(as.character(eir$date), "%m-%d-%y")
> > > > >>>
> > > > >>> If that doesn't work, you'll need to post something reproducible.
> > > > >>>
> > > > >>> Duncan Murdoch
> > > > >>>
> > > > >>> I also need to create weekdays from this date variable but until
> > > > >>> i
> > > get
> > > > >>>> this
> > > > >>>> resolved i cant find a weekday. For weekday i have used:
> > > > >>>> eir$week<- (eir$date)
> > > > >>>> eir$week<- weekdays(as.Date(eir$week))
> > > > >>>> class(eir$week)
> > > > >>>> eir$week<- as.factor(eir$week)
> > > > >>>> head(eir$week)
> > > > >>>>
> > > > >>>> Head of this eir$week results again as expected in <NA> but
> > > > >>>> shows
> > > > Levels:
> > > > >>>> Friday Monday Saturday Sunday Thursday Tuesday Wednesday
> > > > >>>>
> > > > >>>> Not sure what i should do here. Kindly suggest.
> > > >
> > > >
> > >
> > >         [[alternative HTML version deleted]]
> > >
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> >
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> >
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