[R] Question about time series

[Peter Dalgaard]

Dennis Fisher <fisher at plessthan.com> writes:

> I have data in the following format:
> 
>  > DATE
> [1] "01/13/2004"
> 
> In order to find the difference between two data points, I presently
> use brute force to calculate the day of the year:
> 
>  > strptime(DATE, format="%m/%d/%Y")$yday
> [1] 12
> 
> Although this works, it may not be robust over different years.  I
> assume that R is sufficiently clever that a much simpler approach
> exists, e.g., can I calculate the number of days since some fixed
> time? Unfortunately, the man pages and FAQ did not lead me to an
> obvious solution.
> 
> Any help appreciated.


> str(as.Date("2004-01-13"))
Class 'Date'  num 12430
> as.Date("2004-01-13") - as.Date("1970-01-01")
Time difference of 12430 days

(Using ISO standard format, others require an explicit format= argument)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
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