Hi,
You can also use either of these:
data$date <- as.Date(data$date,format="%m/%d/%y")
data$Days<-as.vector(sapply(lapply(split(data,data$Person),`[`,2),function(x) difftime(x[,1],x[1,],units="days")))
#or
data$Days<-as.vector(sapply(lapply(split(data,data$Person),`[`,2),function(x) x[,1]-x[1,]))
#or
data$Days<-unlist(lapply(lapply(split(data,data$Person),`[`,2),function(x) difftime(x[,1],x[1,],units="days")))
data
data
#? Person?????? date Days
#1??? bob 2000-01-01??? 0
#2??? bob 2000-01-02??? 1
#3??? bob 2000-01-03??? 2
#4?? dave 2000-01-07??? 0
#5?? dave 2000-01-08??? 1
#6?? dave 2000-01-10??? 3
#7? kevin 2000-01-02??? 0
#8? kevin 2000-01-03??? 1
#9? kevin 2000-01-04??? 2
A.K.
----- Original Message -----
From: Marcel Curlin <cemarcel at u.washington.edu>
To: r-help at r-project.org
Cc:
Sent: Thursday, September 27, 2012 1:16 AM
Subject: [R] Calculating number of elapsed days from starting date
Hi
I have data for events in rows, with columns for person and date. Each
person may have more than one event;
tC <- textConnection("
Person??? date
bob??? 1/1/00
bob??? 1/2/00
bob??? 1/3/00
dave??? 1/7/00
dave??? 1/8/00
dave??? 1/10/00
kevin??? 1/2/00
kevin??? 1/3/00
kevin??? 1/4/00
")
data <- read.table(header=TRUE, tC)
close.connection(tC)
rm(tC)
I would like to add a new column to my dataframe containing the calculated
number of elapsed days from the starting date for each person. So the new
dataframe would read
Person??? date??? Days
bob??? 1/1/00??? 0
bob??? 1/2/00??? 1
bob??? 1/3/00??? 2
dave??? 1/7/00??? 0
dave??? 1/8/00??? 1
dave??? 1/10/00??? 3
kevin??? 1/2/00??? 0
kevin??? 1/3/00??? 1
kevin??? 1/4/00??? 2
Not sure how to do this, tried looking through the forum but didn't find
anything that seemed to apply. Suggestions appreciated.
--
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