calculate time from dates

Hello,

The functions in stackoverflow need a date 'format' argument.

# Functions from
# 
http://stackoverflow.com/questions/1995933/number-of-months-between-two-dates
# with a 'format' argument added
#
# turn a date into a 'monthnumber' relative to an origin
monnb <- function(d, format = "%Y-%m-%d") {
	lt <- as.POSIXlt(as.Date(d, origin="1900-01-01", format = format))
	lt$year*12 + lt$mon
}
# compute a month difference as a difference between two monnb's
mondf <- function(d1, d2, format = "%Y-%m-%d") {
	monnb(d2, format = format) - monnb(d1, format = format)
}

dat1 <- read.table(text = "
ID date
1 4/12/2008
1 4/13/2008
1 5/11/2008
2 3/21/2009
2 4/22/2009
2 8/05/2009
", header = TRUE)

dat2 <- data.frame(ID = dat1$ID, month = mondf("01/01/2008", dat1$date, 
format = "%m/%d/%Y") + 1)

# Now keep just the last one if month diffs are equal
result <- with(dat2, aggregate(month, list(ID, month), FUN = tail, 1))[1:2]
names(result) <- names(dat2)
result

Hope this helps,

Rui Barradas

Em 11-07-2013 11:03, andrija djurovic escreveu:

calculate time from dates

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