https://walczak.org/2018/04/removing-triggers-from-hitachi-etg-4000-fnirs-recordings/

removing_triggers_function.R

# define a function
replace_nth_ETG4000 <- function(x, mark) {
  x <- x %>% group_by(Mark) %>% mutate(Count = row_number()) %>% data.frame()
  double_marks <- which(x$Mark == mark & x$Count %% 2 == 0)
  x$Mark[double_marks] <- 0
  x <- subset(x, select = -Count)
  return(x)
}

# remove second occurrence of Mark 2
df2 <- replace_nth_ETG4000(df, 2)
df2 <- replace_nth_ETG4000(df2, 2)

# reassign block borders
block_borders <- which(df2$Mark == 2)

# plot
plot(df2$CH1.703.6., type = "l", ylab = "Intensity")
abline(v = block_borders, col = "blue")