[R] Find out the day of week for a chron object?

[Dirk Eddelbuettel]

On Mon, Mar 01, 2004 at 10:18:33PM +0530, Ajay Shah wrote:
> I know that this is correct:
> 
>     library(chron)
>     x = dates("01-03-04", format="d-m-y", out.format="day mon year")
>     print(x)
> 
> It gives me the string "01 Mar 2004" which is correct.
> 
> 
> I also know that I can say:
> 
>     print(day.of.week(3,1,2004))
> 
> in which case he says 1, for today is monday.
> 
> 
> My question is: How do I combine these two!? :-) I have a data file
> which is being parsed nicely and read in using the chron() function. I
> need to identify fridays and treat them differently. So I need to run
> the day.of.week function. But day.of.week() doesn't eat a chron
> object, he insists he wants m,d,y. This seems quite odd. Any idea what
> I can do?

Chron and date are older packages, you may want to use the more recent (and
very powerful) DateTimeClasses

> parsedDate <- strptime("01-03-04", "%d-%d-%y")
> format(parsedDate)
[1] "2004-01-03"
> class(parsedDate)
[1] "POSIXt"  "POSIXlt"
> weekdays(parsedDate)
[1] "Saturday"

Start with help(DateTimeClasses), if you ever used the C functions strptime
and strftime it shouldn't be too foreign.  And do look at the mailing list
archives (and/or Google), as questions get answered on this quite often. 

Dirk

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