Is there a way in R or Excel to check that values alternate?

I have a data frame with 60000 rows. In one of the column, the values alternate between "landing" and "take off", as such.

But there are some mistakes, like here in row 5. In this instance, I have the take-off row, but not the landing one.

Is there any way in R or Excel to highlight or select those rows? To be specific: flight numbers are not unique and appear multiple times throughout it.

Thanks!

I tried this:

data() <- read.csv("Flight data.csv")

# Tried to find the positions where values don't alternate correctly
incorrect_positions <- which(data$event[-1] == data$event[-length(data$event)]) + 1

if (length(incorrect_positions) == 0) {
  print("The values in the 'event' column alternate correctly.\n")
} else {
  print("The values in the 'event' column do not alternate correctly at positions:", incorrect_positions, "\n")
}

It did not give me an error, but apparently doesn't correspond to what I want - it kept printing that all the values alternate correctly, when I know for a fact that they don't.

Using as.factor then as.integer to strip of the levels. differences should be -1 or 1; so taking abs will help to identify which are bad ones.

> f <- \(x) c(1L, abs(diff(as.integer(as.factor(x)))))
> f(dat$Movements)
[1] 1 1 1 1 1 0 1
> which(f(dat$Movements) != 1)
[1] 6

Data:

> dput(dat)
structure(list(Movements = c("take-off", "landing", "take-off", 
"landing", "take-off", "take-off", "landing"), Flight.number = c(11L, 
11L, 53L, 53L, 67L, 123L, 123L), Destination = c("Paris", "Paris", 
"Ibiza", "Ibiza", "Mans", "Geneva", "Geneva")), class = "data.frame", row.names = c(NA, 
-7L))