Suppose I have a calendar that goes from April-April. Using R, how do I find out which week number (e.g. 1-52) a date belongs to?

Here is some data:

example_df <- data.frame(
    full_date = as.Date(c("2020-04-01", "2020-04-08", "2021-03-25", "2021-04-02"))
)

I thought of this way which pushes all dates back to January and then recalculates:

    library(lubridate)
    

example_df %>%
  mutate(
    date_obj = as.Date(full_date),
    fiscal_year = ifelse(month(date_obj) < 4, year(date_obj) - 1, year(date_obj)),
    fiscal_year_start = as.Date(paste0(fiscal_year, "-04-01")),
    days_since_fy_start = as.numeric(date_obj - fiscal_year_start),
    fiscal_week = ceiling((days_since_fy_start + 1) / 7)
  )

Is there another way to do this in R?

    get_april_year <- function(dates) {
      dates <- as.Date(dates)
      
      calendar_year <- as.numeric(format(dates, "%Y"))
      month <- as.numeric(format(dates, "%m"))
      
    
      start_year <- ifelse(month < 4, calendar_year - 1, calendar_year)
      
      fiscal_year <- paste0(start_year, "-", start_year + 1)
      
      return(fiscal_year)
    }

test_dates <- as.Date(c("2020-06-02", "2025-02-15", "2020-04-01"))
get_april_year (test_dates)

>Solution :

Update

Now I got your point that you want to start the "year" from a given date, then probably you could use

> as.integer(full_date - full_date[1]) %/% 7 + 1
[1]  1  2 52 53

Previous

You can use %V to present the week number

> full_date <- as.Date(c("2020-04-01", "2020-04-08", "2021-03-25", "2021-04-02"))

> format(full_date, "%V")
[1] "14" "15" "12" "13"

If you type ?strptime, you will see other similar options, e.g., %U and %W, which depends on what you really need.