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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