Hi,
May be this helps:
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
",sep="",header=TRUE,stringsAsFactors=FALSE)
library(mondate)
M1<- mondate(dat1[,2])
M2<- mondate("01/01/2008")
dat1$month<-as.numeric(abs(floor(MonthsBetween(M1,M2))))
dat1
# ID date month
#1 1 4/12/2008 4
#2 1 4/13/2008 4
#3 1 5/11/2008 5
#4 2 3/21/2009 15
#5 2 4/22/2009 16
#6 2 8/05/2009 20
A.K.
----- Original Message -----
From: Gallon Li <gallon...@gmail.com>
To: r-help <r-h...@stat.math.ethz.ch>
Cc:
Sent: Thursday, July 11, 2013 5:56 AM
Subject: [R] calculate time from dates
My data are from 2008 to 2010, with repeated measures for same subjects. I
wish to compute number of months since january 2008.
The data are like the following:
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
...
the date column are in the format "%m/%d/%y". i wish to obtain
ID month
1 4
1 4
1 5
2 15
2 16
2 20
...
also, for the same ID with two identical month, I only want to keep the
last one. can any expert help with this question?
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and provide commented, minimal, self-contained, reproducible code.
