Stevenson, Jonathan wrote:
Hi,

I've just had a problem related to the Date::Calc modules calculation of week numbers, as some of my data suppliers are obviously using a different algorithm to calculate week 1 of a year - they define dates which fall into week 1 of 2003 according to Date::Calc as week 53 of 2002.

I suspect you are looking for ISO-8601, which is the applicable International standard. Also see this very nice FAQ:

http://www.tondering.dk/claus/cal/node6.html#SECTION00680000000000000000

for a discussion of (and formula for) calculating week number.


I need to know the criteria for defining week 1 of a year according to Date::Calc to check which data suppliers match, and which I need to create custom week number generators for. From the documentation, I suspect it might be the week containing the 1si of January, with Monday defined as the first day of a week, but I can't find it confirmed anywhere. Does anyone know what it uses?
According to the prior section of the above FAQ:

http://www.tondering.dk/claus/cal/node6.html#SECTION00670000000000000000

since the first Thusday in January is Jan 2, 2003, that is Week 1 (and hence Date::Calc is "wrong"). Note also the last line of that answer (that this numbering is not used in the US).

HTH

John

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John Peacock
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