Hi,
Try:
dat1<- read.table(text="
ID Date x2 x1????????? x3
56 25-Jun-01 10 2? 126
56 29-Oct-01 10 2? 140
56 18-Mar-02 10 2? 445
56 6-Jun-03 10 2??? 224
56 16-Jan-04? 10 2??? NA
58 10-Jan-02 10.8 1 715
58 26-Dec-03 10.8 1??? NA
",sep="",header=TRUE,stringsAsFactors=FALSE)
?unlist(with(dat1,by(as.Date(Date,format="%d-%b-%y"),ID,FUN=function(x)
c(diff(x),NA))),use.names=FALSE)
#[1] 126 140 445 224? NA 715? NA
#or
unlist(lapply(split(dat1,dat1$ID),function(x)
c(diff(as.Date(x$Date,format="%d-%b-%y")),NA)),use.names=FALSE)
#[1] 126 140 445 224? NA 715? NA
A.K.
________________________________
From: farnoosh sheikhi <farnoosh_81 at yahoo.com>
To: "smartpink111 at yahoo.com" <smartpink111 at yahoo.com>
Sent: Tuesday, July 23, 2013 3:11 PM
Subject: subtracting rows for unique
Hi there,
Hope you are doing well.
I have a data set which looks like below, I want to create a new variable
(x3-here) which subtracts the date for unique ID.
For example for ID 56, the first value is the difference between ?29-Oct, and
25-June.
Thanks for your help and time.
ID Date x2 x1???? ? ? ?x3
56 25-Jun-01 10 2 126
56 29-Oct-01 10 2 140
56 18-Mar-02 10 2 445
56 6-Jun-03 10 2 224
56 16-Jan-04??NA ? ? ? ? ? ? NA
58 10-Jan-02 10.8 1 715
58 26-Dec-03 10.8 1 ? ? ? ? ? ? NA
Best,Farnoosh Sheikhi?
