Create end_time variable on row A from start_time variable on row B-CodePudding

I would like to create an end_time variable for each participant based on their start_times and time_end_of_experiment (minus say 10 ms), but quite unsure how to do this.

Here's a minimal working example

df <- data.frame("subject_nr" = c("1", "1", "1", "2", "2"),
                 "start_time" = c(50, 52, 55, 53, 54.5),
                 "time_end_of_experiment" = c(60, 60, 60, 55.5, 55.5))


  subject_nr start_time time_end_of_experiment
1          1       50.0                   60.0
2          1       52.0                   60.0
3          1       55.0                   60.0
4          2       53.0                   55.5
5          2       54.5                   55.5

Here's what the final product should look like

  subject_nr start_time end_time time_end_of_experiment  
1          1       50.0     51.9                     60
2          1       52.0     54.9                     60
3          1       55.0     59.9                     60
4          2       53.0     54.4                   55.5
5          2       54.5     55.4                   55.5

CodePudding user response：

Here is how we could do it: First use lead to substract 0.1 from lead(start_time) then for the last value in the groups use an ifelse statement to substract 0.1 from time_end_of_experiment:

library(dplyr)

df %>% 
  group_by(subject_nr) %>% 
  mutate(end_time = lead(start_time, default = last(start_time))-.1, .before=3) %>% 
  mutate(end_time = ifelse(start_time == last(start_time), time_end_of_experiment-.1, end_time))

  subject_nr start_time end_time time_end_of_experiment
  <chr>           <dbl>    <dbl>                  <dbl>
1 1                50       51.9                   60  
2 1                52       54.9                   60  
3 1                55       59.9                   60  
4 2                53       54.4                   55.5
5 2                54.5     55.4                   55.5