CODEWITHSUNDEEP
rlubridate
Where's my towel
Where's my towel

Reputation: 601

Day of the year for each day in a given month

I would like to have a function month2doty() in R that, if provided with a number representing a month (e.g. 2 for February), returns a vector containing the day of the year for each day in that month (so 32, 33, 34, …, 59 for February):

> month2doty(2)
 [1] 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

Leap years do not exist in my world. I have provided one possible answer below, but I'm sure there are better solutions?

Upvotes: 2

Views: 112

Answers (2)

Ronak Shah
Ronak Shah

Reputation: 388982

Here is another way to do it in base R. We create a 2-length sequence between the start of the month and the next month and then produce all the dates between them. We use %j in format to display the day of the year for those dates.

month2doty <- function(x) {

  days <- seq(as.Date(paste0(format(Sys.Date(), "%Y"), "-", x, "-01")), 
                       by = "1 month", length.out = 2)
  as.integer(format(seq(days[1], days[2] - 1, by = "day"), "%j"))
}

month2doty(2)
# [1] 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 
#     54 55 56 57 58 59

month2doty(12)
# [1] 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 
#     354 355 356 357 358 359 360 361 362 363 364 365

Or another variation using seq only once and days_in_month from lubridate

library(lubridate)

month2doty <- function(x) {
   days <- as.Date(paste0(format(Sys.Date(), "%Y"), "-", x, "-01")) 
   as.integer(format(seq(days, days + days_in_month(x) - 1, by = "day"), "%j"))
}

If we don't want to treat leap years differently, we can hardcode the year (as in OP)

month2doty <- function(x) {
  days <- seq(as.Date(paste0("2015-", x, "-01")), by = "1 month", length.out = 2)
  as.integer(format(seq(days[1], days[2] - 1, by = "day"), "%j"))
}

and 

month2doty <- function(x) {
   days <- as.Date(paste0("2015-", x, "-01")) 
   as.integer(format(seq(days, days + days_in_month(x) - 1, by = "day"), "%j"))
}

Upvotes: 1

Where&#39;s my towel
Where&#39;s my towel

Reputation: 601

My current solution to this the somewhat awkward construction of a lookup table each time the function is called:

month2doty <- function(mon=1){
  require(lubridate)
  alldays <- seq(from=ymd("2015-01-01"), length.out=365, by="days")
  lookuptable <- data.frame(month=month(alldays), day=day(alldays), doty=yday(alldays) )
  monthdata <- subset(lookuptable, lookuptable$month==mon)
  return(monthdata$doty)
}

month2doty(2)

It works just fine like that, but I wonder if there's a cleaner solution that I'm missing here.

Upvotes: 0

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