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One method for adding unique identifiers as columns when dealing with recurring rows in a data frame in R is to use the row_number() function from the dplyr package.

Here's an example:

library(dplyr)

# create example data frame with recurring rows
df <- data.frame(name = c("John", "Mary", "John", "Bob", "Mary"),
                 age = c(30, 25, 30, 40, 25))

# add unique identifier column
df <- df %>% 
  group_by(name, age) %>% # group by columns to identify recurring rows
  mutate(id = row_number()) # use row_number() to add unique identifier column

df

This will output:

# A tibble: 5 x 3
# Groups:   name, age [4]
  name    age    id
  <chr> <dbl> <int>
1 John     30     1
2 Mary     25     1
3 John     30     2
4 Bob      40     1
5 Mary     25     2

The id column contains unique identifiers for each group of rows that have the same values in the name and age columns.