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strptime, date and conversion of week number into POSIX

6 messages · Patrick Giraudoux, Bert Gunter, Uwe Ligges +1 more

Original
Patrick Giraudoux
# 
Dear all,

I have a trouble trying to convert dates? given in character to POSIX. 
The date is expressed as a year then the week number e.g. "2020-01" 
(first week of 2020). I thought is can be converted as following:

strptime(mydate,format="%Y-%W")

%W refering to the week of the year as decimal number (00?53) using 
Monday as the first day of week (and typically with the first Monday of 
the year as day 1 of week 1), as indicated in the doc.

However, I got this result, with the month fixed to 02 (february) and 
day 22 (only the year is? converted correctly):

strptime(mydate,format="%Y-%W") [1] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [5] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [9] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [13] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [17] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [21] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [25] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [29] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [33] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [37] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [41] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [45] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [49] "2020-02-22 CET" "2020-02-22 CET" 
"2020-02-22 CET" "2020-02-22 CET" [53] "2020-02-22 CET" "2021-02-22 CET" 
"2021-02-22 CET" "2021-02-22 CET" [57] "2021-02-22 CET" "2021-02-22 CET" 
"2021-02-22 CET"

You'll find below a dump of "mydate" you can copy and paster if you need 
a try

Any hint welcome...

Best,

Patrick

mydate <-
c("2020-01", "2020-02", "2020-03", "2020-04", "2020-05", "2020-06",
"2020-07", "2020-08", "2020-09", "2020-10", "2020-11", "2020-12",
"2020-13", "2020-14", "2020-15", "2020-16", "2020-17", "2020-18",
"2020-19", "2020-20", "2020-21", "2020-22", "2020-23", "2020-24",
"2020-25", "2020-26", "2020-27", "2020-28", "2020-29", "2020-30",
"2020-31", "2020-32", "2020-33", "2020-34", "2020-35", "2020-36",
"2020-37", "2020-38", "2020-39", "2020-40", "2020-41", "2020-42",
"2020-43", "2020-44", "2020-45", "2020-46", "2020-47", "2020-48",
"2020-49", "2020-50", "2020-51", "2020-52", "2020-53", "2021-01",
"2021-02", "2021-03", "2021-04", "2021-05", "2021-06")
Patrick Giraudoux
# 
Sorry to answer to myself, but the format was clearly incorrect in the 
previous post. It should read, refering to the 1th day of the week:

strptime(paste0(mydate,"-1"),format="%Y-%W-%u")

It converts better, but with a NA on week 53
[1] "2020-01-06 CET"  "2020-01-13 CET"  "2020-01-20 CET"  "2020-01-27 CET"
  [5] "2020-02-03 CET"  "2020-02-10 CET"  "2020-02-17 CET"  "2020-02-24 CET"
  [9] "2020-03-02 CET"  "2020-03-09 CET"  "2020-03-16 CET"  "2020-03-23 CET"
[13] "2020-03-30 CEST" "2020-04-06 CEST" "2020-04-13 CEST" "2020-04-20 CEST"
[17] "2020-04-27 CEST" "2020-05-04 CEST" "2020-05-11 CEST" "2020-05-18 CEST"
[21] "2020-05-25 CEST" "2020-06-01 CEST" "2020-06-08 CEST" "2020-06-15 CEST"
[25] "2020-06-22 CEST" "2020-06-29 CEST" "2020-07-06 CEST" "2020-07-13 CEST"
[29] "2020-07-20 CEST" "2020-07-27 CEST" "2020-08-03 CEST" "2020-08-10 CEST"
[33] "2020-08-17 CEST" "2020-08-24 CEST" "2020-08-31 CEST" "2020-09-07 CEST"
[37] "2020-09-14 CEST" "2020-09-21 CEST" "2020-09-28 CEST" "2020-10-05 CEST"
[41] "2020-10-12 CEST" "2020-10-19 CEST" "2020-10-26 CET"  "2020-11-02 CET"
[45] "2020-11-09 CET"  "2020-11-16 CET"  "2020-11-23 CET"  "2020-11-30 CET"
[49] "2020-12-07 CET"  "2020-12-14 CET"  "2020-12-21 CET"  "2020-12-28 CET"
[53] NA                "2021-01-04 CET"  "2021-01-11 CET"  "2021-01-18 CET"
[57] "2021-01-25 CET"  "2021-02-01 CET"  "2021-02-08 CET"
Warning message:
In strptime(paste0(pays$year_week, "-1"), format = "%Y-%W-%u") :
   (0-based) yday 369 in year 2020 is invalid


Any idea on how to handle this ?




Le 22/02/2021 ? 15:26, Patrick Giraudoux a ?crit?:

  
  


  


      

    

    

      
      

        


  

        

      Bert Gunter
    

    

      
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I think the relevant info from ?strptime is:

"For strptime the input string need not specify the date completely: it is
assumed that unspecified seconds, minutes or hours are zero, and an
unspecified year, month or day is the current one. (However, if a month is
specified, the day of that month has to be specified by %d or %e since the
current day of the month need not be valid for the specified month.) Some
components may be returned as NA (but an unknown tzone component is
represented by an empty string)."

I think this means that your strings cannot be converted by strptime() as
essential info is missing. Input from those with more date-time expertise
on this point would be welcome, however.

Cheers,
Bert
Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Mon, Feb 22, 2021 at 6:27 AM Patrick Giraudoux <

        
patrick.giraudoux at univ-fcomte.fr> wrote:

        

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Uwe Ligges
    

    

      
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That monday does not exist. FOr the week before:

strptime(paste0("2020-52","-1"),format="%Y-%W-%u")
[1] "2020-12-28"

One week later is no longer in 2020, so there is no 53th week.

Best,
Uwe Ligges

        
On 22.02.2021 16:15, Patrick Giraudoux wrote:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Patrick Giraudoux
    

    

      
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Thanks Uwe and? Bert,
I got the essential now, and can manage. Date handling stays quite a 
challenge with a variable number of weeks in a year, but I can 
understand why. Means eye-control (or NA detection) of strptime 
conversion stays necessary...
Best,
Patrick


Le 22/02/2021 ? 17:09, Uwe Ligges a ?crit?:

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      PIKAL Petr
    

    

      
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Hallo Patrick

I found quite usefull for working with weeks package ISOweek

https://cran.r-project.org/web/packages/ISOweek/index.html

Cheers.
Petr