[R] Replace rows in dataframe based on values in other columns

[arun]

Hi,
dat1<- read.table(text="
Restaurant owner purchase_date
            23 Chuck 3/4/2011
            23 Chuck 3/4/2011
            23 Chuck 3/4/2011
            23 Chuck 3/4/2011
            23 Bob        1/1/2013
            23 Bob        1/1/2013
            23 Bob         1/1/2013
            15 Hazel 4/11/2010
            15 Hazel 4/11/2010
            15 Hazel 4/11/2010
            15 Hazel 4/11/2010
            17 Pete 9/2/2012
            17 Pete 9/2/2012
            17 Pete 9/2/2012
            17 Pete 9/2/2012
",sep="",header=TRUE,stringsAsFactors=FALSE) 
#if the dates are in order for the Restaurant group, 
 dat1$Current_Owner<-with(dat1,ave(owner,Restaurant,FUN=function(x) tail(x,1)))
 dat1
#   Restaurant owner purchase_date Current_Owner
#1          23 Chuck      3/4/2011           Bob
#2          23 Chuck      3/4/2011           Bob
#3          23 Chuck      3/4/2011           Bob
#4          23 Chuck      3/4/2011           Bob
#5          23   Bob      1/1/2013           Bob
#6          23   Bob      1/1/2013           Bob
#7          23   Bob      1/1/2013           Bob
#8          15 Hazel     4/11/2010         Hazel
#9          15 Hazel     4/11/2010         Hazel
#10         15 Hazel     4/11/2010         Hazel
#11         15 Hazel     4/11/2010         Hazel
#12         17  Pete      9/2/2012          Pete
#13         17  Pete      9/2/2012          Pete
#14         17  Pete      9/2/2012          Pete
#15         17  Pete      9/2/2012          Pete
 


If the order is different:
dat2<- read.table(text="
Restaurant owner purchase_date
           23 Bob        1/1/2013
            23 Bob        1/1/2013
            23 Bob         1/1/2013
            23 Chuck 3/4/2011
            23 Chuck 3/4/2011
            23 Chuck 3/4/2011
            23 Chuck 3/4/2011
            15 Hazel 4/11/2010
            15 Hazel 4/11/2010
            15 Hazel 4/11/2010
            15 Hazel 4/11/2010
            17 Pete 9/2/2012
            17 Pete 9/2/2012
            17 Pete 9/2/2012
            17 Pete 9/2/2012
",sep="",header=TRUE,stringsAsFactors=FALSE) 
dat2New<-unsplit(lapply(split(dat2,dat2$Restaurant), FUN= function(x) {x1<-x[order(as.Date(x$purchase_date,format="%m/%d/%Y")),]; x1$Current_Owner<- tail(x1$owner,1); x1}),dat2$Restaurant)
 
 rownames(dat2New)<- 1:nrow(dat2New)
 dat2New
#   Restaurant owner purchase_date Current_Owner
#1          23 Chuck      3/4/2011           Bob
#2          23 Chuck      3/4/2011           Bob
#3          23 Chuck      3/4/2011           Bob
#4          23 Chuck      3/4/2011           Bob
#5          23   Bob      1/1/2013           Bob
#6          23   Bob      1/1/2013           Bob
#7          23   Bob      1/1/2013           Bob
#8          15 Hazel     4/11/2010         Hazel
#9          15 Hazel     4/11/2010         Hazel
#10         15 Hazel     4/11/2010         Hazel
#11         15 Hazel     4/11/2010         Hazel
#12         17  Pete      9/2/2012          Pete
#13         17  Pete      9/2/2012          Pete
#14         17  Pete      9/2/2012          Pete
#15         17  Pete      9/2/2012          Pete
A.K. 




>I have the following data frame including restaurants (id#) ,owner and
 purchase date. Sometimes the restaurant changes ownership, but for 
>analysis purposes I want to create another column which only keeps the 
name of the latest owner, this is determined by the "purchase date". How
 >can I create this new column? In this example restaurant 23 changes 
hand on 1/1/2013, so I want to include only the new owner's name (Bob) 
as >the current owner for all rows for this restaurant as shown below. If
 the restaurant does not change hands, keep the same name for the 
"current >owner" column as the "owner" column. 
>
>Thanks, 
>Johnny 
>
>
>
>Restaurant	owner	purchase date 
  >          23	Chuck	3/4/2011 
 >           23	Chuck	3/4/2011 
  >          23	Chuck	3/4/2011 
   >         23	Chuck	3/4/2011 
   >         23	Bob	        1/1/2013 
   >         23	Bob	        1/1/2013 
   >         23	Bob	         1/1/2013 
   >         15	Hazel	4/11/2010 
   >         15	Hazel	4/11/2010 
   >         15	Hazel	4/11/2010 
   >         15	Hazel	4/11/2010 
  >          17	Pete	9/2/2012 
 >           17	Pete	9/2/2012 
 >           17	Pete	9/2/2012 
  >          17	Pete	9/2/2012 
  >                      
>Restaurant	owner	purchase date	Current owner 
>            23	Chuck	3/4/2011	        Bob 
>            23	Chuck	3/4/2011	        Bob 
>            23	Chuck	3/4/2011	        Bob 
>            23	Chuck	3/4/2011	        Bob 
>            23	Bob	1/1/2013	                Bob 
>            23	Bob	1/1/2013	                Bob 
>            23	Bob	1/1/2013	                Bob 
>            15	Hazel	4/11/2010	        Hazel 
>            15	Hazel	4/11/2010	        Hazel 
>            15	Hazel	4/11/2010	        Hazel 
>            15	Hazel	4/11/2010	        Hazel 
>            17	Pete	9/2/2012	        Pete 
>            17	Pete	9/2/2012	        Pete 
>            17	Pete	9/2/2012	        Pete 
>            17	Pete	9/2/2012	        Pete