[R] histogramming dates

Michael A. Miller mmiller3 at iupui.edu
Tue May 28 23:57:15 CEST 2002

I'd like to make a plot showing frequency of an event.  The data
is in a data from that includes Year, Month and Day (of month)
fields, so I created a Date with ISOdate(Year, Month, Day,
tz='').  I can plot frequencies for the year 2002 with

  > thisyear <- Date[Year==2002]
  > hist( thisyear, xaxt='n' )
  > axis.POSIXct( 1, at=seq(min(thisyear), max(thisyear), by="month"),
                 format='%b %Y' )

Now I want to specify the histogram breaks so that there is one
bin per month, so I tried this:

  > hist( thisyear,
       breaks=ISOdate( rep(2002,12), seq(12), rep(1,12), tz='' ),
       xaxt='n' )

That resulted in an error message that said:

  Error in Ops.POSIXt(1e-07, mean(h)) : * not defined for POSIXt objects

Can anyone suggest a way to do this?  Or another method for
plotting this sort of month by month frequency plot?  For a
single year I could histogram the month, but I'd like to be able
to span any date range, including multiple years.


Michael A. Miller                               mmiller3 at iupui.edu
  Imaging Sciences, Department of Radiology, IU School of Medicine
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