number of Mondays

Or for those not allergic to reading help, see ?weekdays .

Just how hard do you have to work to miss that?  E.g. ??day works.

On Thu, 15 Jan 2009, Peter Dalgaard wrote:

Carlos Hernandez wrote:

dear All,
i'm trying to calculate the number of Mondays, Tuesdays, etc that  
each
month within a date range has. I have time series data that spans 60
months and i want to calculate the number of Mondays, Tuesdays,  
Wed, etc
of each month. (I want to control for weekly seasonality but my  
data is
monthly).

Is there an easy way to to this in R? or is there a package i  
could use?
i did some quick search in the help files and R sites but could  
not find
any answers.

i appreciate any hint you could give,

This is where POSIXlt objects are useful:

unlist(unclass(as.POSIXlt(ISOdate(1959,3,11))))

sec   min  hour  mday   mon  year  wday  yday isdst
  0     0    12    11     2    59     3    69     0

Which means that I was born on a Wednesday (wday==3) in March  
(mon==2)
(some of the fields count from 0 and others, like mday, from 1;
presumably some UNIX vendor back in the Stone Age got their
implementation turned into a standard...).

This allows you to do stuff like:

dd <- seq(Sys.Date(),as.Date("2009-3-11"),1)
dd <- as.POSIXlt(dd)
with(dd, table(mon,wday))

 wday
mon 0 1 2 3 4 5 6
0 2 2 2 2 3 3 3
1 4 4 4 4 4 4 4
2 2 2 2 2 1 1 1

which I think is pretty much what you were looking for.

thanks.

Carlos

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