I have written a set of functions for POSIXt objects that I would
like to offer for consideration for use in base R. They augment and
extend existing functions. Briefly,
## pretty.ct function(x,specs=pretty.ct.specs)
## round.ct function(x, tstr='1 min' )
## axis.ct function(side,x,specs=NULL,...)
## parse.timeint function(dv)
## parse.tstr function(tstr)
## pretty.ct.specs default value for the 'specs' argument of
pretty.ct()
pretty.ct() is a 'pretty' function for POSIXt objects. It implements
my idea of what is pretty, which is dependent on the time scale, and
with the default specs prefers hours in multiples of 3, 6, or 12, and
days in multiples of 7 or 14.
round.ct() serves the same purpose as round.POSIXt(), but allows
rounding to multiples of the time unit, i.e., '15 min' , '2
hours',
and the like.
axis.ct() serves the same purpose as axis.POSIXct() but selects tick
values and intervals using pretty.ct(). Surprisingly, axis.ct() is
significantly faster than axis.POSIXct() when passed a long vector.
The two parse functions translate strings like '10 min' or '36
h' to
other more useable forms. These are based on code found in an early
version of seq.POSIXct(), written, I believe, by Prof. Ripley.
A few examples are below.
If there is interest, I can send the source code, and will write Rd
files for them.
-Don
> hrs <- 3600
> dys <- 24*hrs
##
## time range 60 hours
## pretty.ct() chooses 3 hours as a pretty interval
##
nhr <- 60> t1 <- ISOdatetime(2002,6,14,0,0,0)+hrs*runif(5,0,nhr)
> pretty.ct(t1)
[1] "2002-06-15 03:00:00 PDT" "2002-06-15 06:00:00 PDT"
"2002-06-15
09:00:00 PDT" "2002-06-15 12:00:00 PDT"
[5] "2002-06-15 15:00:00 PDT" "2002-06-15 18:00:00 PDT"
"2002-06-15
21:00:00 PDT" "2002-06-16 00:00:00 PDT"
[9] "2002-06-16 03:00:00 PDT" "2002-06-16 06:00:00 PDT"
"2002-06-16
09:00:00 PDT"
> t1 <- sort(t1)
> cbind(format(t1),format(round.ct(t1,'6 h')))
[,1] [,2]
[1,] "2002-06-15 02:49:03" "2002-06-15 00:00:00"
[2,] "2002-06-15 04:40:25" "2002-06-15 06:00:00"
[3,] "2002-06-15 11:12:29" "2002-06-15 12:00:00"
[4,] "2002-06-15 14:47:43" "2002-06-15 12:00:00"
[5,] "2002-06-16 09:01:32" "2002-06-16 12:00:00"
##
## time range 65 days
## pretty.ct() chooses 1 week as a pretty interval
##> ndy <- 65
> t2 <- ISOdatetime(2002,6,24,0,0,0)+ndy*dys*(0:5)/5
> pretty.ct(t2)
[1] "2002-06-23 PDT" "2002-06-30 PDT" "2002-07-07
PDT" "2002-07-14
PDT" "2002-07-21 PDT" "2002-07-28 PDT" "2002-08-04
PDT"
[8] "2002-08-11 PDT" "2002-08-18 PDT" "2002-08-25
PDT"> cbind(format(t2),format(round.ct(t2,'1 w')))
[,1] [,2]
[1,] "2002-06-24" "2002-06-23"
[2,] "2002-07-07" "2002-07-07"
[3,] "2002-07-20" "2002-07-21"
[4,] "2002-08-02" "2002-08-04"
[5,] "2002-08-15" "2002-08-18"
[6,] "2002-08-28" "2002-08-25"
##
## the parse functions
##> parse.tstr('36 h')
$secs
[1] 129600
$nunits
[1] 36
$units
[1] "hours"
$tstr
[1] "36 h"
> parse.timeint('36 h')
[1] 129600
##
## speed comparison
##> t8 <-
>structure(sort(runif(100000,1017820800,2*1017820800)),class=c('POSIXt','POSIXct'))
> plot(t8,1:100000,xaxt='n',pch=3)
> system.time(axis.ct(1,t8))
[1] 0.65 0.02 0.69 0.00 0.00> system.time(axis.POSIXct(1,t8))
[1] 11.94 0.00 12.07 0.00 0.00
> version
_
platform sparc-sun-solaris2.7
arch sparc
os solaris2.7
system sparc, solaris2.7
status
major 1
minor 7.1
year 2003
month 06
day 16
language R
--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
