cal.yr {Epi} | R Documentation |
Dates are converted to a numerical value, giving the calendar year as
a fractional number. 1 January 1970 is converted to 1970.0, and other
dates are converted by assuming that years are all 365.25 days long,
so inaccuracies may arise, for example, 1 Jan 2000 is converted to
1999.999. Differences between converted values will be 1/365.25 of the
difference between corresponding Date
objects.
cal.yr( x, format="%Y-%m-%d", wh=NULL ) as.Date.cal.yr( x, ... ) as.Date.numeric( x, ..., unit="d" )
x |
A factor or character vector, representing a date in format
format , or an object of class
Date ,
POSIXlt ,
POSIXct ,
date ,
dates or
chron (the latter two requires the chron package).
If x is a data frame, all variables in the data-frame
which are of one the classes mentioned are converted to class cal.yr .
See arguemt wh , though. |
format |
Format of the date values if x is factor or character.
If this argument is supplied and x is a datafame, all
character variables are converted to class cal.yr .
Factors in the dataframe will be ignored. |
wh |
Indices of the variables to convert if x is a data frame.
Can be either a numerical or character vector. |
unit |
Which units are the date measured in, "y" for years,
"d" for days. |
... |
Arguments passed on from other methods. |
cal.yr
returns a numerical vector of the same length as
x
, of class c("cal.yr","numeric")
. If x
is a data frame
a dataframe with some of the columns converted to class "cal.yr"
is
returned.
as.Date.cal.yr
and as.Date.numeric
return Date
objects.
Bendix Carstensen, Steno Diabetes Center & Dept. of Biostatistics, University of Copenhagen, bxc@steno.dk, http://www.pubhealth.ku.dk/~bxc
# Charcter vector of dates: birth <- c("14/07/1852","01/04/1954","10/06/1987","16/05/1990", "01/01/1996","01/01/1997","01/01/1998","01/01/1999") # Proper conversion to class "Date": birth.dat <- as.Date( birth, format="%d/%m/%Y" ) # Converson of character to class "cal.yr" bt.yr <- cal.yr( birth, format="%d/%m/%Y" ) # Back to class "Date": bt.dat <- as.Date( bt.yr ) # Numerical calculation of days since 1.1.1970: days <- Days <- (bt.yr-1970)*365.25 # Blunt assignment of class: class( Days ) <- "Date" # Then data.frame() to get readable output of results: data.frame( birth, birth.dat, bt.yr, bt.dat, days, Days, round(Days) )