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2011 Mar 10
2
within group sequential subtraction
...the time between separate observations for a group of individuals. My data: data <- structure(list(group = c("IND1", "IND1", "IND2", "IND2", "IND2", "IND3", "IND4", "IND5", "IND6", "IND6"), date_obs = structure(c(6468, 7063, 9981, 14186, 14372, 5129, 9767, 11168, 10243, 10647), class = "Date")), .Names = c("group", "date_obs"), row.names = c(NA, 10L), class = "data.frame") So I start with: group date_obs 1 IND1 1987-09-17 2 IND1 1989-05-04 3...