mondate-methods: Create an instance of the mondate class
In mondate: Keep Track of Dates in Terms of Months

Description Usage Arguments Details Methods See Also Examples

All purpose mondate constructor / coercer.

    mondate(x, 
      displayFormat = getOption("mondate.displayFormat", 
                                default = .get.default.displayFormat()), 
      timeunits = getOption("mondate.timeunits",
                            default = .get.default.timeunits()),
      ...)
    ## S4 method for signature 'mondate'
mondate(x, displayFormat, timeunits, formatFUN, ...)
    ## S4 method for signature 'numeric'
mondate(x, displayFormat, timeunits, ...)
    ## S4 method for signature 'Date'
mondate(x, displayFormat, timeunits, ...)
    ## S4 method for signature 'POSIXt'
mondate(x, displayFormat, timeunits, ...)
    ## S4 method for signature 'character'
mondate(x, displayFormat = "keep", timeunits, format, ...)
    ## S4 method for signature 'array'
mondate(x, displayFormat, timeunits, ...)
    ## S4 method for signature 'missing'
mondate(x, displayFormat, timeunits, ...)
    ## S4 method for signature 'ANY'
mondate(x, displayFormat, timeunits, ...)

`x`	an R object to convert to a `mondate`. Can be another `mondate`, a character representing a date, a date, a numeric, or an object which converts to a numeric with as.numeric(x). More details below.
`displayFormat`	character string representing the date format with which to display the `mondate`. The default.displayFormat is determined at the time an instance is created according to Sys.getlocale("LC_TIME"): if it contains the words "United States", the default will be "%m/%d/%Y" (MM/DD/YYYY), otherwise "%Y-%m-%d" (YYYY-MM-DD). Other choices are "%m-%d-%Y" and "%Y/%m/%d". See "Details" section for how to change defaults.
`timeunits`	character string "months" (default), "years", or "days" indicating the units in which date arithmetic will be carried out.
`formatFUN`	format function for converting a mondate to character. In case of conversion from `mondate`, default is to inherit the value.
`format`	format string for converting a character to a Date (using `as.Date, x, format, ...`) from which the mondate value is determined.
`...`	arguments to be passed to other methods.

Package users can change the default values of displayFormat and timeunits using options() with the names "mondate.displayFormat" and "mondate.timeunits", respectively. Warning! Use with care! No checks are performed if and when the options are established. It is up to the user to ensure the new defaults are valid – displayFormat must be appropriate for formatting dates in R and timeunits must be one of "months", "years", or "days". See an example below.

signature(x = "mondate"): For mondate x, this could be a way to copy a mondate and perhaps change the mondate's displayFormat or timeunits slots in the process. For any class that extends mondate, use of this method will return the underlying mondate class without additional slots (if any) of the subclass.
signature(x = "numeric"): For numeric x, the simplest case is when timeunits = "months", in which case the value of x and properties displayFormat and timeunits are simply stored. If timeunits = "years" then it is presumed that the value of x represents the number of years since the beginning of the millennium, in which case the value of x is multiplied by 12 and then stored. If timeunits = "days" then it is presumed that the value of x represents the number of days since the beginning of the millennium, in which case the value is calculated using as.Date. Note that infinite values of x are allowed, helpful in actuarial ("at ultimate") longitudinal, and time series modeling.
signature(x = "Date")
signature(x = "POSIXt"): For a date x, as.POSIXlt is used to convert to an ISO standard date, from which the number of months of that day since the beginning of the millennium is calculated.
signature(x = "character"): If format is provided, then that format is used to attempt to convert the character value to a date. Otherwise, characters are converted to dates using the first format found in the set of valid formats that successfully converts the first non-NA entry in x, and that format is retained as the displayFormat of the result unless the user explicitly provides a value for displayFormat. The current set of valid formats is "%m/%d/%Y", "%m-%d-%Y", "%Y-%m-%d", and "%Y/%m/%d". If any entries of x do not convert successfully, those entries get the value NA and a warning is issued. Finally, if format is not provided and none of the valid formats successfully converts x to a date, then as a last resort the character string is attempted to be coerced to a numeric and then to a mondate.
signature(x = "factor"): The character method is run on as.character(x).
signature(x = "array"): If an object x is an array, then this method enables the mondate to inherit its shape. After that, other "signatures" take over.
signature(x = "missing"): Enables the call mondate() to work. Useful for prototypes, e.g. Body of method is simply new("mondate").
signature(x = "ANY"): For any other class of x an attempt will be made to convert to Date ("as.Date(x)"). If unsuccessful, an attempt will be made to convert to numeric; if successful, a warning will be issued to check the results relative to the numeric conversion, otherwise execution will be stopped.

POSIXt, yearmon, yearqtr

mondate("1-31-2010") # Jan. 31, 2010
mondate(60)          # 60 months after 12/31/1999, so Dec. 31, 2004
dat <- as.Date("2010-1-31")
(M <- mondate(dat))    # Jan. 31, 2010
x <- 12 * 1:6
mondate(x)           # first 6 yearends in 2000's
y <- x + 12
mondate(cbind(x,y))  # bounding dates of first 6 years of millennium
(y <- mondate(1:6,timeunits="years")) # first 6 yearends, 'years' timeunits 
# The results of date arithmetic on y will be displayed in "years".
# E.g., the differences of y can be calculated as:
tail(y,-1) - head(y,-1)# vector of five 1's, with "timeunits" attribute = "years"
as.numeric(x)
as.numeric(y)        # the underlying numeric representations are the same

# Demonstrating "infinite" dates
y <- c(y,Inf)
y                    # last element shows as Inf
tail(y,-1) - head(y,-1)# last element is now infinity

# The zoo examples point out a difference between zoo and mondate.
#   zoo assumes that the zero-th part of a month or quarter is the first
#   day of the month or quarter, whereas mondate assumes that it is 
#   the instant before the first day of the month or quarter.
# Since frac=0 is zoo's as.Date coersion default, a month or quarter in 
#   zoo's sense converts to the end of the first day rather than
#   the beginning.
library(zoo)
x <- ts(1:10, frequency = 4, start = c(1959, 2)) # starting 2nd qtr of 1959
x
# There is no method for class 'ts' so x is coerced (successfully) 
#   because that class has an as.Date method, but with a warning.
# The result is a vector of length 10 representing the close of business
#   at the end of the first day of each of the given quarters.
mondate(x)      

# The yearmon class will identify any day in June 2010 with that month.
as.yearmon("2010-6-15") 
mondate(as.yearmon("2010-6-15"))         # end of first day of June 2010
mondate(as.yearmon("2010-6-15", frac=1)) # end of  last day of June 2010
mondate(as.yearqtr("2010-2", frac=1))    # same

# The if missing, displayFormat will be determined from the character input
x <- mondate("2010-12-31")
x               # x displays in the input European format
# The provided, displayFormat must match the format of the character input
#   or NA's will result.
mondate("2010-12-31", displayFormat = "%m-%d-%Y") # results in NA

# Always display x using just the year
x <- mondate(as.Date("2012-3-1"), displayFormat="%Y")
x                # shows as the year 2012, but month and day are nevertheless retained
month(x)         # 3
day(x)           # 1

# Change the default displayFormat to only display the year and month
options(mondate.displayFormat = "%Y-%m")
y <- mondate(as.Date("2013-12-31"))
y
# mondate: timeunits="months"
# [1] 2013-12
# Previous mondate instances retain their display formats:
x
# mondate: timeunits="months"
# [1] 2012