On Jul 31, 2009, at 4:46 PM, liujb wrote:
Dear R users:
I have a vector of dates as follows:
t <- c("2007-01-05", "2007-05-14", "2007-12-28", "2008-01-09",
"2008-04-24",
"2009-02-14")
I'd like to calculate number of days between those dates (time
interval).
How to do it?
That is not a vector of dates, but rather a character vector.
Observe:
t <- c("2007-01-05", "2007-05-14", "2007-12-28", "2008-01-09",
"2008-04-24",
"2009-02-14")
class(t)
# [1] "character"
diff(t)
#Error in r[i1] - r[-length(r):-(length(r) - lag + 1)] :
# non-numeric argument to binary operator
Try:
t2 <- as.Date(t)
class(t2)
#[1] "Date"
t2
# [1] "2007-01-05" "2007-05-14" "2007-12-28" "2008-01-09" "2008-04-24"
"2009-02-14"
?diff
diff(t2)
#Time differences in days
#[1] 129 228 12 106 296
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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