[R] Julian Dates

[Gabor Grothendieck]

Assuming you want to find a whole number months and quarters:

   require(chron)

   z <- chron( SLDATX, format="y-m-d" )

   months <- with( month.day.year(z), 12*(year-1986)+month-1 )

   quarters <- months %/% 3

--- 
Date: Tue, 16 Dec 2003 13:58:13 +1300 (NZDT) 
From: Ko-Kang Kevin Wang <kwan022 at stat.auckland.ac.nz>
To: Gabor Grothendieck <ggrothendieck at myway.com> 
Cc: <ligges at statistik.uni-dortmund.de>, <r-help at stat.math.ethz.ch> 
Subject: Re: [R] Julian Dates 

 
 
Thanks! chron() is very useful indeed.

Just out of interest, is it possible to do, say in this case, the number 
of months (or quarters) after January 1986? i.e. use a different time 
interval?

On Mon, 15 Dec 2003, Gabor Grothendieck wrote:

> What you can do to handle this timezone problem is either to use
> POSIXt with GMT or use chron (which does not use timezones so 
> can't cause problems like this):
> 
> Suppose:
> 
> SLDATX <- c( "1986-01-06", "1986-01-17", "1986-02-02", "1986-02-04",
> ,"1986-02-04", "1986-02-21", "1986-03-06", "1986-03-25",
> ,"1986-04-06", "1986-04-10" )
> 
> # then using POSIXt in the GMT timezone:
> 
> TIMESOLD <- as.numeric( julian( as.POSIXlt( SLDATX, tz="GMT" ),
> origin = as.POSIXct( "1986-01-01", tz = "GMT" ) ) )
> 
> # or the alternative using chron:
> 
> require(chron)
> TIMESOLD2 <- as.numeric( chron( SLDATX, format="y-m-d", 
> origin = c( month = 1, day = 1, year = 1986 ) ) )
> 
> all.equal(TIMESOLD,TIMESOLD2)
> 

-- 
Cheers,

Kevin

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