从R中的timeDate获取借出

Question

I would like to get all Lent Fridays from 2010 to 2020. I am currently using timeDate to get holidays such as Easter, Good Friday, and Ash Wednesday. As follows

aw <- as.Date(AshWednesday(year = 2010:2020))
gf <- as.Date(GoodFriday(year = 2010:2020))

I can also get fixed holidays that don't come with the package. For example

mg <- as.Date(AshWednesday(year = 2010:2020)-1) #Mardi Gras
cm <- as.Date(seq(ymd('2010-05-05'),ymd('2020-05-05'), by = '1 year')) #cinco de mayo

But I am struggling to get all Lent Fridays per year.

Note: Lent begins on the Sunday that follows Ash Wednesday and lasts for 40 days.

As posted below, the following code worked:

library(dplyr)
library(purrr)
library(tidyr)
library(lubridate)

tibble(aw) %>% 
    mutate(aw_sunday = aw + lubridate::days(0)) %>%  #Find the first Sunday after each Ash Wednesday
    mutate(extra_days = map(aw_sunday, function(x) x + lubridate::days(1:40))) %>% #Find all series of 40 days after each sunday
    unnest %>% 
    mutate(week_day = lubridate::wday(extra_days, label = TRUE)) %>% #Find all the day names
    filter(week_day == 'Fri') %>%  # Filter out the fridays
    pull(extra_days)

I changed days(4) to days(0) because I think lent Fridays actually start immediately after Ash Wednesday, not skipping a week. I pulled the Note above from Wikipedia under "the Ambrosian Rite". I guess there is a difference.

Answer 1

Here's one way to do it:

library(dplyr)
library(purrr)
library(tidyr)
library(lubridate)

tibble(aw) %>% 
    mutate(aw_sunday = aw + lubridate::days(4)) %>%  #Find the first Sunday after each Ash Wednesday
    mutate(extra_days = map(aw_sunday, function(x) x + lubridate::days(1:40))) %>% #Find all series of 40 days after each sunday
    unnest %>% 
    mutate(week_day = lubridate::wday(extra_days, label = TRUE)) %>% #Find all the day names
    filter(week_day == 'Fri') %>%  # Filter out the fridays
    pull(extra_days)

Answer 2

If you don't want to use lubridate, you can use the base seq.Date function:

gf <- as.Date(GoodFriday(year = 2010:2020))
lentFridays <- lapply(gf, function(x)seq.Date(x, length.out = 6, by = "-7 days"))

and to pretty it up:

lentFridays <- data.frame(lentFridays)
names(lentFridays) <- paste0("Year", 2010:2020)

Answer 3

If Lent begins on the Sunday after Ash Wednesday, then all subsequent Fridays are those that are 9, 16, ..., 44 days after Ash Wednesday. You can use the days or ddays functions in lubridate to add time durations to individual dates. Since you have a vector of dates, we can store the Lent Fridays in a list.

library(lubridate)
lent_fridays <- lapply(aw, function(x) x + days(seq(9, 44, by =7)))

eg, for 2018, the Lent Fridays are the following dates.

[[9]]
[1] "2018-02-23" "2018-03-02" "2018-03-09" "2018-03-16" "2018-03-23"
[6] "2018-03-30"