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rpanel

Create dummies for followup visits

I have a simple data structure with id and time-series indicator (prd). I would like to create a dummy variable for followup visits "fup", which is equal to 0 if a patient has no more visits and 1 if a patient has more visits in the future.

How would I go about doing this?

id<- c(1, 1, 1, 2, 3, 3)
prd <- c(1, 2, 3, 1, 1, 2)

df <- data.frame(id=id, prd=prd)

Desired output:

  id prd fup
1  1   1   1
2  1   2   1
3  1   3   0
4  2   1   0
5  3   1   1
6  3   2   0
Solution

  • We can check if the current row is the last row in each group. In base R, 

    df$fup <- with(df, ave(prd, id, FUN = function(x) seq_along(x) != length(x)))
df

#  id prd fup
#1  1   1   1
#2  1   2   1
#3  1   3   0
#4  2   1   0
#5  3   1   1
#6  3   2   0

    Similarly in dplyr, 

    library(dplyr)
df %>%  group_by(id) %>%  mutate(fup = +(row_number() != n()))

    and data.table

    library(data.table)
setDT(df)[, fup := +(seq_along(prd) != .N), by = id]