Basic date time arithmetics operations

Fan · 2003-04-28T20:46:43Z

>>Also for the function seq.dates (or seq.POSIXt), the >>case for by="months" would be more useful if it takes >>the situation of the end of month into account. >>For example, >> >>> seq(ISOdate(2002,1,31), by="months", length=3) >> >>"2002-01-31 13:00:00 CET" >>"2002-03-03 13:00:00 CET" >>"2002-03-31 13:00:00 CET" >> >>rather than >> >>"2002-01-31 13:00:00 CET" >>"2002-02-28 13:00:00 CET" >>"2002-03-31 13:00:00 CET" > >I don't think that's a well-defined request. What would you want from

Fan

Mon, Apr 28, 2003 1:46 PM

1. When we shift or add/substract n month(s) from a date, n should be
refleted in the month level (or more precisely YYYYMM level) arithmetics 
between the resulting date and the original date,

2. For the day of month level, some sort of alignment should be considered. 

The simplest way would be like what's doing the Oracle SQL function 
add_months(d,n): If d is the last day of the month or if the resulting month 
has fewer days than the day component of d, then the result is the last day 
of the resulting month. Otherwise, the result has the same day component as d.

In a time series specialized software like Fame, the function SHIFTMTH
seems having more sophisticated options.

Best
--
Fan


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