CODEWITHSUNDEEP
rdate
PAC
PAC

Reputation: 5366

Is it possible to count the distance between two dates in months or years?

The difftime() function makes it easy to compute the difference between two dates in days or in weeks but there is no option to compute the difference in months or in years. Is there any reason for that ? Would you know any function which would perform this task ?

Upvotes: 3

Views: 6131

Answers (2)

IRTFM
IRTFM

Reputation: 263352

The POSIXlt datetime-class is a list with several extraction methods including months and quarter. (The months function returns a character value so you need to extract the mon item from the list which is an integer.) If you want to subtract the months values from successive items in a vector it would be something along the lines of:

PLvec <- as.POSIXlt(vec)
PLvec[-1]$mon - PLvec[-length(PLvec)]$mon

vec <- seq(from = as.Date('2012-1-2'),
           to = as.Date('2012-7-5'), 
           by="60 days")
 PLvec <- as.POSIXlt(vec)
 PLvec[-1]$mon - PLvec[-length(PLvec)]$mon
#[1] 2 2 1

You should educate yourself about POSIXlt classed items, because they are really lists and do not play well with data.frame storage.

dput(as.POSIXlt(Sys.time()))
structure(list(sec = 24.0051879882812, min = 5L, hour = 9L, mday = 30L, 
    mon = 9L, year = 113L, wday = 3L, yday = 302L, isdst = 1L), .Names = c("sec", 
"min", "hour", "mday", "mon", "year", "wday", "yday", "isdst"
), class = c("POSIXlt", "POSIXt"), tzone = c("", "PST", "PDT"
))

Upvotes: 4

Matthew Plourde
Matthew Plourde

Reputation: 44614

From the comments: Months and years aren't precise time units, that is, their lengths vary (months can have 28, 29, 30, 31 days. Years can have 365 or 366). If you want to fix a value for one of these units (e.g., month = 30 days, year = 365 days), you can just divide your difftimes in days by the fixed value to get the difference in the units you want. Or if you just want something like the number of complete months between two dates, you could do this

date1 = as.Date('2012-1-2')
date2 = as.Date('2012-7-5')
length(seq(from=date1, to=date2, by='month')) - 1
# [1] 6

or for weeks:

length(seq(from=date1, to=date2, by='week')) - 1
# [1] 26

Upvotes: 15

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