如果在R中跟随特定值，则删除这些值

Question

I am fairly new to R and I would need your help. I have a dataset, which looks like the following example:

id   type   timespan 
1    yes    2016-07-30 06:22:24
1    no     2016-07-30 09:12:16
1    yes    2016-07-30 10:42:20
2    no     2016-07-30 18:46:15
1    yes    2016-07-30 19:56:54
2    yes    2016-07-30 20:44:00

I would now like to keep only those "yes" values that are not followed by a "no" value based on the ID. This is how I would expect my output to be:

id   type   timespan 
1    yes    2016-07-30 10:42:20
1    yes    2016-07-30 19:56:54
2    yes    2016-07-30 20:44:00

Is there a way how to do this in R?

Thank you for your help!

Answer 1

Something like:

library(dplyr)

 df %>%
  group_by(id) %>% 
  filter(type == 'yes' & coalesce(lead(type) != 'no', T))

In data.table , you could do:

library(data.table)

setDT(df)[, .SD[(type != "no" & (shift(type, type = "lead") != "no" | is.na(shift(type, type = "lead"))))], by = id]