[R] How to get week of the year, scale 1-52?

[Peter Dalgaard]

Eik Vettorazzi wrote:
> But usually weeks start with a Monday. So what should happen when new 
> year isn't on a Monday? format(days, "%W") puts the first Monday of the 
> year in the first week, which makes sense.
>
>   
No it doesn't. Well, it does, but it will only match our planning 
calendars in some years. For ISO dates, the rule is that the week 
crossing New Year belongs to the year containing the majority of its 
days. Consider the following:

 > x <- as.Date(paste(1999:2009, "-12-31", sep=""))
 > cbind(date=format(x), ISOdate=format(x, format="%G: Week %V, day %u"))
      date         ISOdate              
 [1,] "1999-12-31" "1999: Week 52, day 5"
 [2,] "2000-12-31" "2000: Week 52, day 7"
 [3,] "2001-12-31" "2002: Week 01, day 1"
 [4,] "2002-12-31" "2003: Week 01, day 2"
 [5,] "2003-12-31" "2004: Week 01, day 3"
 [6,] "2004-12-31" "2004: Week 53, day 5"
 [7,] "2005-12-31" "2005: Week 52, day 6"
 [8,] "2006-12-31" "2006: Week 52, day 7"
 [9,] "2007-12-31" "2008: Week 01, day 1"
[10,] "2008-12-31" "2009: Week 01, day 3"
[11,] "2009-12-31" "2009: Week 53, day 4"


> hth.
>
> Lauri Nikkinen schrieb:
>   
>> Yeah, that's correct. I can accept that there is more than 52 weeks in
>> a year (:-)) but it's hard to accept that the first week e.g in this
>> example is 00 (year 2008). Should the first week be the first one, 1?
>>
>> -Lauri
>>
>> 2008/3/18, John Kane <jrkrideau at yahoo.ca>:
>>   
>>     
>>> 365/7 != 52.  You have more than 52 weeks in each
>>> year.
>>>
>>>
>>> --- Lauri Nikkinen <lauri.nikkinen at iki.fi> wrote:
>>>
>>>     
>>>       
>>>> R users,
>>>>
>>>> I have a vector of dates
>>>>
>>>> days <- seq(as.Date("2007/1/1"),
>>>> as.Date("2008/1/31"), "days")
>>>>
>>>> and I would like to have week numbers from 1 to 52
>>>> for each year. How
>>>> do I do that? Now I get 00-53 using
>>>>
>>>> format(days, "%W")
>>>>
>>>>       
>>>>         
>>>>> range(format(days, "%W"))
>>>>>         
>>>>>           
>>>> [1] "00" "53"
>>>>
>>>> I have read "Date and Time Classes in R" (R news
>>>> 01/04 by Gabor
>>>> Grothendieck and Thomas Petzoldt) with no help.
>>>>
>>>> Thanks
>>>> Lauri
>>>>
>>>> ______________________________________________
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>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained,
>>>> reproducible code.
>>>>
>>>>       
>>>>         
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>>>     
>>>       
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>   
>>     
>
>   


-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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