Remove 3rd iteration of duplicate

General
2

You can achieve the required functionality with dplyr::lag() function; consider the example below:

What it does is it computes a technical column called duplicate, which is based on the value of current name column, compared to the previous row and previous by two. TRUE for all three values equal, FALSE for different (note the NA in first row where lag is undefined).

You can then use it easily for eliminating the offending rows, if so desired.

library(dplyr)

animals <- tibble(row = 1:6,
                  name = c("cat", "dog", "cat", "dog", "dog", "dog"))

animals <- animals %>% 
   mutate(duplicate = ifelse(name == lag(name, n = 1) 
                             & name == lag(name, n = 2), T, F))

print(animals)

    row name  duplicate
  <int> <chr> <lgl>    
1     1 cat   NA       
2     2 dog   FALSE    
3     3 cat   FALSE    
4     4 dog   FALSE    
5     5 dog   FALSE    
6     6 dog   TRUE
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