R help - Jul 2010 - How to plot a histogram of weekday frequencies in a list of dates?

Question from an [R] novice...
Hi,
I have a vector of date/times like the one shown below (a truncated
sample of a much longer list...)
> dates[1:4]
[1] "2006-03-16 08:41:00" "2006-03-16 10:28:00"
"2006-03-16 11:03:00"
[4] "2006-03-16 11:04:00"

I would like to generate a weekday histogram showing the frequency of
dates falling on each weekday. I know that the function weekdays()
gives me the weekday for each date in my vector, but the hist()
function can't plot non-numeric values. There should be a function to
allow me to do this simply. Any thoughts?

After having done this, I would also like to bin my histogram in 12 hr
periods (Mon 7am - 7pm; Mon 7pm - Tues 7am; Tues 7am - 7pm; Tues
7pm-Wed 7am... etc) so that I can plot the frequency of event
occurrences within each 12 hour period over the course of a week. Any
help would be greatly appreciated. Thanks

David

Hope it works.

## Create a sample of dates 
dates <- sample(seq(ISOdate(2009,1,1), ISOdate(2009,12,31),
"hour"),1000)

## Create 14 labels for barplot("Mon AM","Mon PM",etc.)
labels <- format(seq(ISOdate(2010,7,11,5), ISOdate(2010,7,18,4), "12
hours"),"%a %p")

## Use table function to calculate the frequency of each time intervel
## Use format "%w %p" to get the weekday name and AM/PM indicator of
the
dates
## Minus 12*60*60 seconds to change AM interval from 0-12AM to 7AM-7PM
barplot(table(format((dates-12*60*60), "%w %p")),names.arg=labels)


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Correction:

## Minus 7*60*60 seconds to change AM interval from 0-12AM to 7AM-7PM
barplot(table(format((dates-7*60*60), "%w %p")),names.arg=labels)

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