[R] extract week from date

Erich Neuwirth erich.neuwirth at univie.ac.at
Fri Apr 12 01:01:49 CEST 2002

from the calendar faq

5.7. What is the week number?

International standard ISO-8601 (mentioned in section 5.6) assigns a
number to each week of the year. A week that lies partly in one year
and partly in another is assigned a number in the year in which most
of its days lie. This means that

         Week 1 of any year is the week that contains 4 January,

or equivalently

         Week 1 of any year is the week that contains the first
         Thursday in January.

Most years have 52 weeks, but years that start on a Thursday and leap
years that start on a Wednesday have 53 weeks.

Note: This week numbering system is not used in the United States.


can somebody from the united states tell us how weeks are numbered there?

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