I am trying to compare 2 different fields across consecutive rows on a data frame in R and indicate the ones that are different. Below is the input data:-

```
Start End
1 Atl Bos
2 Bos Har
3 Har NYC
4 Stf SFO
5 SFO Chi
```

I am trying to establish a chain of movement and where the End doesn't match up to the Start of the next row I want to indicate that row. So for the above I would indicate row 4 as below:-

```
Start End Ind
1 Atl Bos Y
2 Bos Har Y
3 Har NYC Y
4 Stf SFO N
5 SFO Chi Y
```

I am pretty new to R, I have tried looking up this problem but cant seem to find a solution. Any help is appreciated.

An alternative would be:

```
> Ind <- as.character(dat$Start[-1]) == as.character(dat$End [-length(dat$End)])
> dat$Ind <- c(NA, ifelse(Ind==TRUE, "Y", "N"))
> dat
Start End Ind
1 Atl Bos <NA>
2 Bos Har Y
3 Har NYC Y
4 Stf SFO N
5 SFO Chi Y
```

Note that your first item should be `<NA>`