Re: Date Difference - Qsn

Eric Sosman <esosman@acm-dot-org.invalid>
Mon, 28 May 2007 17:25:02 -0400
alij wrote:


I have two dates and I want to find the difference in years between
them. I noticed the Date class doesn't provide me with such a function
like datediff. Will appreciate any pointers how I can go about this.

     The "difference in years" could mean a number of
different things, for example:

     - If T1 is 31-Dec-2007 23:59:59 and T2 is 01-Jan-2008
       00:00:01, are T1 and T2 a year apart (they occur in
       different calendar years), or about 0.0000000634 years
       apart (two seconds)?

     - Same situation, but assuming that the chronology wizards
       add a leap second 23:59:60 to the end of December 2007.

     - Same situation, but assuming that T1 is given in EDT
       (UTC-5) and T2 in UTC.

     - If T1 is 01-Jan-2008 00:00:00 UTC and T2 is 01-Jan-2009
       00:00:00 UTC, are they one year apart, or a year and a
       day apart, or a year and 18 hours (approximately) apart?

     - If T1 is the birthday of Iannis Xenakis (29-May-1922) and
       T2 is the date of his death (04-Feb-2001), how many years
       apart are T1 and T2? Keep in mind that Xenakis was a Greek
       composer, so the dates are given according to the calendars
       used in Greece at the relevant times. Greece switched from
       the Julian to the Gregorian calendar in 1923, so in that year
       15-Feb was followed by 01-Mar; 1923 was only 352 days long in
       Greece, about 3.56% shorter than most other years. Does that
       affect your answer?

     In short, before you can get a useful answer you need to
clarify your question. Exactly what do you mean by "the difference
in years" between two moments?

Eric Sosman

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