Match/group duplicate rows (indices)

Question

How can I efficiently match/group the indices of duplicated rows?

Let\'s say I have this data set:

set.seed(14)
dat <- data.frame(mtc         


        

Answer 1

We can use dplyr. Using a similar methodology as @AnandaMahto's post, we create a row index column name (add_rownames(), group by all the columns, we filter the dataset with number of rows in each group greater than 1, summarise the 'rowname' to a list and extract that list column.

library(dplyr)
add_rownames(dat) %>% 
      group_by_(.dots= names(dat)) %>% 
      filter(n()>1) %>%
      summarise(rn= list(rowname))%>%
      .$rn
 #[[1]]
 #[1] "3"  "7"  "8"  "10" "11"

 #[[2]]
 #[1] "2"  "13"

 #[[3]]
 #[1] "1" "4" "5" "6" "9"