从星期日开始一年中的第一天，并在星期六结束一年中的最后一天

Question

I have recently encountered a problem in R dealing with the dates. The last day of 2015 (2015-12-31) falls on Thursday, meaning last week of the year only contains 5 days if I consider Sunday as the start day of my week. Now, I would like 2016-01-01 and 2016-01-02, which fall on Friday and Saturday, to be associated with week 53, and start week 1 on 2016-01-03, which falls on Sunday.

require(lubridate)
range <- seq(as.Date('2015-12-26'), by = 1, len = 10)
df <- data.frame(range)
df$WKN <- as.numeric(strftime(df$range, format = "%U")) + 1
df$weekday <- weekdays(df$range)
df$weeknum <- wday(df$range)

This would give me the following result:

df:
range      WKN   weekday   weeknum
2015-12-26  52  Saturday       7
2015-12-27  53    Sunday       1
2015-12-28  53    Monday       2
2015-12-29  53   Tuesday       3
2015-12-30  53 Wednesday       4
2015-12-31  53  Thursday       5
2016-01-01   1    Friday       6
2016-01-02   1  Saturday       7
2016-01-03   2    Sunday       1
2016-01-04   2    Monday       2

Now I would like to have my dataframe as follows:

df:
range      WKN   weekday   weeknum
2015-12-26  52  Saturday       7
2015-12-27  53    Sunday       1
2015-12-28  53    Monday       2
2015-12-29  53   Tuesday       3
2015-12-30  53 Wednesday       4
2015-12-31  53  Thursday       5
2016-01-01  53    Friday       6
2016-01-02  53  Saturday       7
2016-01-03   1    Sunday       1
2016-01-04   1    Monday       2

Could anyone point me to a direction to automate that so that I don't have to change the code every year?

Answer 1

We can use cumsum on a logical vector

df$WKN <- unique(df$WKN)[cumsum(df$weeknum==1) +1]
df$WKN
#[1] 52 53 53 53 53 53 53 53  1  1

Answer 2

If you check out ?strptime , there are a few different week number tokens available for use with format . Here %V almost works, except it starts the week on Monday, so add one to adjust:

df$WKN <- as.integer(format(df$range + 1, '%V'))

df
##         range WKN   weekday weeknum
## 1  2015-12-26  52  Saturday       7
## 2  2015-12-27  53    Sunday       1
## 3  2015-12-28  53    Monday       2
## 4  2015-12-29  53   Tuesday       3
## 5  2015-12-30  53 Wednesday       4
## 6  2015-12-31  53  Thursday       5
## 7  2016-01-01  53    Friday       6
## 8  2016-01-02  53  Saturday       7
## 9  2016-01-03   1    Sunday       1
## 10 2016-01-04   1    Monday       2

Or if you're using dplyr like the tag suggests,

library(dplyr)

df %>% mutate(WKN = as.integer(format(range + 1, '%V')))

which returns the same thing. The isoweek function of lubridate is equivalent, so you could also do

library(lubridate)

df$WKN <- isoweek(df$range + 1)

or

df %>% mutate(WKN = isoweek(range + 1))

both of which return identical results to the as.integer(format(...)) versions.

Answer 3

Considering that you are using lubridate , I also wanted to give you a lubridate solution. You also asked for a solution that works with other years. Here goes:

adjust_first_week<- function(year){

    first <- floor_date(dmy(paste0("1-1-", year)), "year") 
    two_weeks <- c(first - days(7:1), first + days(0:6))

    df <- data.frame(date = two_weeks,
               day_of_week = weekdays(two_weeks),
               day_of_year = yday(two_weeks),
               week_of_year = week(two_weeks))

    last_weekend <- which(df$day_of_week == "Sunday")[2] -1
    df$adjust_week <- df$week_of_year
    if(last_weekend ==7) return(df)
    else{
      df$adjust_week[8:last_weekend] <- rep(53,length(8:last_weekend))
    }
    return(df)
  }

1. Takes a numeric year, and takes the first day of that year.
2. Creates a two week period by appending a week on either side of 1/1/year.
3. Calculates various summary statistics for that year for your edification.
4. Picks out the second Sunday. By design 1/1/year is always the 8th entry.
5. If Sunday is the first day of the month, it doesn't do anything.
6. Otherwise it overwrites the week of the year so that the first week of the year starts on the second Sunday.

Here is the results for

adjust_last_week(2016)
         date day_of_week day_of_year week_of_year adjust_week
1  2015-12-25      Friday         359           52          52
2  2015-12-26    Saturday         360           52          52
3  2015-12-27      Sunday         361           52          52
4  2015-12-28      Monday         362           52          52
5  2015-12-29     Tuesday         363           52          52
6  2015-12-30   Wednesday         364           52          52
7  2015-12-31    Thursday         365           53          53
8  2016-01-01      Friday           1            1          53
9  2016-01-02    Saturday           2            1          53
10 2016-01-03      Sunday           3            1           1
11 2016-01-04      Monday           4            1           1
12 2016-01-05     Tuesday           5            1           1
13 2016-01-06   Wednesday           6            1           1
14 2016-01-07    Thursday           7            1           1