Truncating dates (and other date-time manipulations)

One last item that could be of use:

?timeBasedSeq

Lets you create ranges in any standard format, with simple ISO style
formatting. The level of detail you specify is interpreted as the resolution
that is desired.

e.g.

timeBasedSeq(2000/2008)

[1] "2000-01-01" "2001-01-01" "2002-01-01" "2003-01-01" "2004-01-01"
[6] "2005-01-01" "2006-01-01" "2007-01-01" "2008-01-01"

timeBasedSeq(2000/200012)

[1] "Jan 2000" "Feb 2000" "Mar 2000" "Apr 2000" "May 2000" "Jun 2000"
 [7] "Jul 2000" "Aug 2000" "Sep 2000" "Oct 2000" "Nov 2000" "Dec 2000"

timeBasedSeq(2000/200012, 'Date')

[1] "2000-01-01" "2000-02-01" "2000-03-01" "2000-04-01" "2000-05-01"
 [6] "2000-06-01" "2000-07-01" "2000-08-01" "2000-09-01" "2000-10-01"
[11] "2000-11-01" "2000-12-01"

timeBasedSeq(2000/20000115)

[1] "2000-01-01" "2000-01-02" "2000-01-03" "2000-01-04" "2000-01-05"
 [6] "2000-01-06" "2000-01-07" "2000-01-08" "2000-01-09" "2000-01-10"
[11] "2000-01-11" "2000-01-12" "2000-01-13" "2000-01-14" "2000-01-15"

timeBasedSeq(2000/2000010110)

[1] "2000-01-01 00:00:00 CST" "2000-01-01 01:00:00 CST"
 [3] "2000-01-01 02:00:00 CST" "2000-01-01 03:00:00 CST"
 [5] "2000-01-01 04:00:00 CST" "2000-01-01 05:00:00 CST"
 [7] "2000-01-01 06:00:00 CST" "2000-01-01 07:00:00 CST"
 [9] "2000-01-01 08:00:00 CST" "2000-01-01 09:00:00 CST"
[11] "2000-01-01 10:00:00 CST"

I'm still not entirely sure I follow the desired usage, as the original
post made no reference to ggplot2, but as Gabor mentioned the yearmon etc
stuff is quite useful.

If you are formatting arbitrary precision dates, take a look at
axTicksByTime in xts.  Both xts and quantmod use it for plotting.  The
core calculation is from ?endpoints

I think the effect is what you desire --- though the logic of the function
may be more than you want/need.  I use it within the package(s) to make
intelligent breaks given the periodicity of the data.

Some examples are at:   http://www.quantmod.com http://www.quantmod.com 

My presentation slides from July's Rmetrics conference in Switzerland are
posted here:  http://www.quantmod.com/Rmetrics2008/
http://www.quantmod.com/Rmetrics2008/ 

Most of the functions you have written are somewhere within xts already. 
At least the functionality is. See the vignette: 
http://cran.r-project.org/web/packages/xts/index.html
http://cran.r-project.org/web/packages/xts/index.html 

Jeff  

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