Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Prof Brian Ripley
This is completely wrong: min _is_ defined for date-times: min(.leap.seconds) [1] "1972-07-01 01:00:00 BST" Please do study the posting guide and do your homework before posting: you seem unaware of what the POSIXct class is, so ?DateTimeClasses is one place you need to start. And method

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Gabor Grothendieck
min does work for POSIXct and Date too: > ct <- ISOdatetime(2008, 1, 1:10, 0, 0, 0) > min(ct) [1] "2008-01-01 EST" > min(as.Date(ct)) [1] "2008-01-01" On Mon, Sep 8, 2008 at 6:57 PM, Adam D. I. Kramer <[EMAIL PROTECTED]> wrote: > Hi Erich, > > Since min() is defined for numbers and not dates,

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Adam D. I. Kramer
Hi Erich, Since min() is defined for numbers and not dates, the problem is in the min() function. min() is converting from date format to number format. Your best bet is to make this conversion explicit...such that it is reversable. So, convert the date into UTC, then UTC to seconds since epoch,

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Gabor Grothendieck
> I would be glad, if someone knew a more elegant way to extract the rows with > minimum/earliest date per subject. > > > Erich > > > -Ursprüngliche Nachricht- > Von: jim holtman [mailto:[EMAIL PROTECTED] > Gesendet: Montag, 8. September 2008 14:24 > A

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Prof Brian Ripley
ataframes. Erich -Ursprüngliche Nachricht- Von: Dr Eberhard Lisse [mailto:[EMAIL PROTECTED] Gesendet: Montag, 8. September 2008 15:43 An: Erich Studerus Cc: r-help@r-project.org Betreff: Re: [R] How to preserve date format while aggregating Erich, how does the data look, when it comes

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Erich Studerus
dataframes. Erich -Ursprüngliche Nachricht- Von: Dr Eberhard Lisse [mailto:[EMAIL PROTECTED] Gesendet: Montag, 8. September 2008 15:43 An: Erich Studerus Cc: r-help@r-project.org Betreff: Re: [R] How to preserve date format while aggregating Erich, how does the data look, when it comes f

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Dr Eberhard Lisse
ows with > minimum/earliest date per subject. > > > Erich > > > -Ursprüngliche Nachricht- > Von: jim holtman [mailto:[EMAIL PROTECTED] > Gesendet: Montag, 8. September 2008 14:24 > An: Erich Studerus > Cc: r-help@r-project.org > Betreff: Re: [R] How to

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread jim holtman
t;. > I would be glad, if someone knew a more elegant way to extract the rows with > minimum/earliest date per subject. > > > Erich > > > -Ursprüngliche Nachricht- > Von: jim holtman [mailto:[EMAIL PROTECTED] > Gesendet: Montag, 8. September 2008 14:24 > An:

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread Erich Studerus
re elegant way to extract the rows with minimum/earliest date per subject. Erich -Ursprüngliche Nachricht- Von: jim holtman [mailto:[EMAIL PROTECTED] Gesendet: Montag, 8. September 2008 14:24 An: Erich Studerus Cc: r-help@r-project.org Betreff: Re: [R] How to preserve date form

Re: [R] How to preserve date format while aggregating

2008-09-08 Thread jim holtman
Try changing the 'class' of the numeric result back to Date: > x <- as.Date('2008-09-08') > x [1] "2008-09-08" > y <- as.numeric(x) > y [1] 14130 > str(y) num 14130 > class(y) <- "Date" > y [1] "2008-09-08" > str(y) Class 'Date' num 14130 > On Mon, Sep 8, 2008 at 6:38 AM, Erich Studerus <[EMAI

[R] How to preserve date format while aggregating

2008-09-08 Thread Erich Studerus
Hi I have a dataframe in which some subjects appear in more than one row. I want to extract the subject-rows which have the minimum date per subject. I tried the following aggregate function. attach(dataframe.xy) aggregate(Date,list(SubjectID),min) Unfortunately, the format of the Date-column c