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Calculating number of elapsed days from starting date

4 messages · Marcel Curlin, Rolf Turner, Berend Hasselman +1 more

Marcel Curlin
# 
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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Rolf Turner
#
On 27/09/12 17:16, Marcel Curlin wrote:
X <- data
X$date <- with(X,as.Date(date,format="%m/%d/%y"))
X$Days <- unlist(with(X,tapply(date,Person,function(x){x-x[1]})))

And then if you *really* want to keep that shaganappi date format:

X$date <- data$date
X
# Giving:
Person    date Days
1    bob  1/1/00    0
2    bob  1/2/00    1
3    bob  1/3/00    2
4   dave  1/7/00    0
5   dave  1/8/00    1
6   dave 1/10/00    3
7  kevin  1/2/00    0
8  kevin  1/3/00    1
9  kevin  1/4/00    2

BTW:  You really *shouldn't* call your data "data".  See:

     fortune("dog")

         cheers,

             Rolf Turner
Berend Hasselman
#
On 27-09-2012, at 07:16, Marcel Curlin <cemarcel at u.washington.edu> wrote:

            

      
      
      
    

        
You could do this

DF$realdate <- as.Date(as.character(DF$date),format="%m/%d/%y")
DF$Days <- ave(as.numeric(DF$realdate), by=DF$Person, FUN=function(x) x-x[1])

If you don't want the as.character then you should add stringsAsFactors=FALSE to the read.table argument list.

Berend

  
  


  


      

    

    

      
      

        


  

        

      arun
    

    

      
      #
    

  


  

      
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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View this message in context: http://r.789695.n4.nabble.com/Calculating-number-of-elapsed-days-from-starting-date-tp4644333.html
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