Defines a "WeekDays" constant and a "dailyCalendar" function

dailyCalendar.R

WeekDays <- function(startOn = "Monday", abbreviate = FALSE) {
  WD <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
  x <- match(startOn, WD)
  WD <- WD[c(x:7, setdiff(1:7, x:7))]
  if (isTRUE(abbreviate)) {
    substring(WD, 0, 3)
  } else WD
}


dailyCalendar <- function(startDate = Sys.Date(), days = 30, startOn = "Monday", fancy = FALSE) {
  require(reshape2)
  inDailyTs <- ts(as.character(seq(as.Date(startDate),
                                   length.out = days, by = 1)),
                  frequency = 7)
  temp <- data.frame(
    weekday = factor(weekdays(as.Date(as.character(inDailyTs))), WeekDays(startOn)),
    date = inDailyTs, 
    month = format(as.Date(as.character(inDailyTs)), "%B"),
    day = format(as.Date(as.character(inDailyTs)), "%d"),
    year = format(as.Date(as.character(inDailyTs)), "%Y"),
    stringsAsFactors = FALSE)
  temp$week <- cumsum(temp$weekday == startOn)
  
  if (isTRUE(fancy)) {
    A <- paste(temp$month, temp$year)
    X <- split(temp, factor(A, unique(A), ordered=TRUE))
    lapply(X, function(y) {
      dcast(y, week ~ weekday, value.var = "day", fill = "", drop=FALSE)[WeekDays(startOn)]
    })
  } else {
    dcast(temp, week ~ weekday, value.var = "date", fill = "")[WeekDays(startOn)]
  }
}

It might be interesting to modify the Weekdays function so that it returns weekdays in the language of the locale. I think this would do it.

WD<-strftime(seq(as.Date('2013-11-18'),(as.Date('2013-11-18')+6),by=1),'%A')

But then startsOn would have to modified to either be an integer, and to handle if the user inputs a day of week in a non-English language.

@nograpes, I thought about that but I have not had much time to look into how locale settings work in R. I'll check out your suggestion when I have some time.