[R] Truncating dates (and other date-time manipulations)

hadley wickham h.wickham at gmail.com
Fri Sep 12 18:16:34 CEST 2008

On Fri, Sep 12, 2008 at 10:53 AM, Jeff Ryan <jeff.a.ryan at gmail.com> wrote:
> 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.

Well, I said "I need to be able to correct draw date-time scales",
which means I need to be able to deal with a wide range of date time
data types.  I wasn't really aware of xts before - I'll definitely
look into it in more detail.

> 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.

That's exactly what I want!  I've written my own method, but I think
you've done a much nicer job.  (Although I draw minor grid lines as
well)  I'll definitely look at using that function in a future version
of ggplot2.

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

Very nice - however, I'm philosophically opposed to special purpose
plotting functions!

> 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

Including the ceiling and floor functions?  That's what I'm really
interested in.



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