Mark Beginning and End of Runs in R

Question

I have the following table and want to make a "Beginning" and "End" column with T/F values:

Trigger	Beginning	End
1	T	F
1	F	F
0	F	T
1	T	F
0	F	T
1	T	F
1	F	F

How can this be done in R?

Many thanks

Answer 1

Base:

df <- data.frame(Trigger = c(1, 1, 0, 1, 0, 1, 1))
df$Beginning <- df$Trigger & !c(0, df$Trigger[-nrow(df)]) 
df$End <- !df$Trigger & c(0, df$Trigger[-nrow(df)]

tidyverse:

mutate(
  df, 
  Beginning = Trigger & !lag(Trigger, default = FALSE),
  End = !Trigger & lag(Trigger, default = TRUE)  # May want to use FALSE depending on use case.
)