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>

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