How to find the longest duplicate sequence in a tibble column?

Question

I updated my question because I need one more column to my output tible.

I have the following tibble:

library(tibble)

my_tbl <- tribble(
  ~year, ~event_id, ~winner_id, 
  2011,      "A",     4322,
  2012,      "A",     4322,
  2013,      "A",     4322,
  2014,      "A",     5478,
  2015,      "A",     4322,
  2011,      "B",     4322,
  2012,      "B",     7893,
  2013,      "B",     7893,
  2014,      "B",     2365,
  2015,      "B",     3407,
  2011,      "C",     5556,
  2012,      "C",     5556,
  2013,      "C",     1238,
  2014,      "C",     2391,
  2015,      "C",     2391,
  2011,      "D",     4219,
  2012,      "D",     7623,
  2013,      "D",     8003,
  2014,      "D",     2851,
  2015,      "D",     0418
)

I would like to find out the most wins in a row by event id. The result I'm looking for would look like this:

results_summary_tbl <- tribble( ~event_id, ~most_wins_in_a_row, ~number_of_winners, ~winners, ~years, "A", 3, 1, "4322", "4322 = (2011, 2012, 2013)", "C", 2, 2, "5556 , 2391", "5556 = (2011, 2012), 2391 = (2014, 2015)", "B", 2, 1, "7893", "7893 = (2012, 2013)", "D", 1, 5, "4219 , 7623 , 8003 , 2851 , 0418", "4219 = (2011), 7623 = (2012), 8003 = (2013), 2851 = (2014), 0418 = (2015)" )

thanks

Answer 1

One dplyr option could be:

my_tbl %>%
 add_count(event_id, rleid = cumsum(winner_id != lag(winner_id, default = first(winner_id)))) %>%
 group_by(event_id) %>%
 summarise(most_wins_in_a_row = max(n),
           number_of_winners = n_distinct(winner_id[n == max(n)]),
           winners = paste0(unique(winner_id[n == max(n)]), collapse = ","))

  event_id most_wins_in_a_row number_of_winners winners                
  <chr>                 <int>             <int> <chr>                  
1 A                         3                 1 4322                   
2 B                         2                 1 7893                   
3 C                         2                 2 5556,2391              
4 D                         1                 5 4219,7623,8003,2851,418

Answer 2

One option to get the longest adjacent similar element after grouping by 'event_id' is with rle. It returns a list of lengths and corresponding values. By creating an logical. expression with max 'lengths', subset the 'values' as well as get the lengths

library(dplyr)
library(purrr)
my_tbl %>% 
   group_by(event_id) %>%
   summarise(rl = list(rle(winner_id)),
            most_wins_in_a_row =  map_int(rl, ~ max(.x$lengths)),
            number_of_winners = map2_int(rl, most_wins_in_a_row, 
                 ~ sum(.x$lengths == .y)), 
           winners = map2_chr(rl, most_wins_in_a_row, 
               ~ toString(.x$values[.x$lengths == .y]))) %>%
   select(-rl)
# A tibble: 4 x 4
#  event_id most_wins_in_a_row number_of_winners winners                    
#  <chr>                 <int>             <int> <chr>                      
#1 A                         3                 1 4322                       
#2 B                         2                 1 7893                       
#3 C                         2                 2 5556, 2391                 
#4 D                         1                 5 4219, 7623, 8003, 2851, 418