[R] histogramming dates

[Don MacQueen]

One way would be to convert to POSIXlt and extract the month element. 
Then you should be able to tabulate the number of events in each 
month, and make a barplot of those.
-Don

At 4:57 PM -0500 5/28/02, Michael A. Miller wrote:
>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.
>
>Mike
>
>--
>Michael A. Miller                               mmiller3 at iupui.edu
>   Imaging Sciences, Department of Radiology, IU School of Medicine
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