Handling dates

I have a problem with some functions handling dates, in packages 'date' and 
'survival' (they seem to be identical). For instance, from the documentation,

--------------------
mdy.date {survival}	

R Documentation

Convert to Julian Dates

Description

Given a month, day, and year, returns the number of days since January 1, 1960.
Usage

mdy.date(month, day, year, nineteen = TRUE, fillday = FALSE,
         fillmonth = FALSE)
----------------------------
but

library(survival)
mdy.date(12, 1, 1977)

[1] 1Dec77

Similar strange results appear in other date-related functions. I plan to 
write functions that converts, eg, "1977-01-31" to the real number 1977.084
and back. What function in  R  does what 'mdy.date' claims to do?

dput(mdy.date(12, 1, 1977))

mdy.date(1, 31, 1977)/365.2425+1960 # or /365.25 if you really want 1977.084

c(as.Date("1977-01-31") - as.Date("0000-01-01"))/365.2425

(as.Date("1977-01-31") - as.Date("0000-01-01"))/365.2425

G??ran Brostr??m <gb at stat.umu.se> writes:

I have a problem with some functions handling dates, in packages 'date' and 
'survival' (they seem to be identical). For instance, from the documentation,

--------------------
mdy.date {survival}	

R Documentation

Convert to Julian Dates

Description

Given a month, day, and year, returns the number of days since January 1, 1960.
Usage

mdy.date(month, day, year, nineteen = TRUE, fillday = FALSE,
         fillmonth = FALSE)
----------------------------
but

library(survival)
mdy.date(12, 1, 1977)

[1] 1Dec77

Similar strange results appear in other date-related functions. I plan to 
write functions that converts, eg, "1977-01-31" to the real number 1977.084
and back. What function in  R  does what 'mdy.date' claims to do?

mdy.date does ...

dput(mdy.date(12, 1, 1977))

structure(6544, class = "date")

mdy.date(1, 31, 1977)/365.2425+1960 # or /365.25 if you really want 1977.084

[1] 1977.085

But with recent R's, as.Date is a better bet:

c(as.Date("1977-01-31") - as.Date("0000-01-01"))/365.2425

[1] 1977.084

(notice that you need the c() to avoid the nonsense of

(as.Date("1977-01-31") - as.Date("0000-01-01"))/365.2425

Time difference of 1977.084 days

)


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Similar strange results appear in other date-related functions. I plan to
write functions that converts, eg, "1977-01-31" to the real number 1977.084
and back. What function in  R  does what 'mdy.date' claims to do?

1970+ mdy.date(12,1,1977)/365.25