Try this:
> data$diff <- ave(as.numeric(data$date_obs), data$group, FUN=function(x)c(NA,
> diff(x)))
> data
group date_obs diff
1 IND1 1987-09-17 NA
2 IND1 1989-05-04 595
3 IND2 1997-04-30 NA
4 IND2 2008-11-03 4205
5 IND2 2009-05-08 186
6 IND3 1984-01-17 NA
7 IND4 1996-
Dear Natalie,
I am sure there are other ways, but one way you can do this is by
applying diff() to each group using tapply() or by(). Because those
return lists, if you want to add it back into your data frame, you can
wrap the whole call in unlist(). Here is an example:
dat <- structure(list(g
Hi Everyone,
I would like to do sequential subtractions within a group so that I know 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 = struc
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