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Group column by regular interval

I'm struggling to solve a seemingly simple task. In this type of data:

df <- data.frame(
  A = c(1,2,3,4,1,2,3,2,2,2,2,1,1,1,1,6,7)
)

I want to add an id variable that groups column A by a regular interval, say, of 5. An additional difficulty is that the number of rows is 17, thus not a multiple of 5:

df <- data.frame(
  A = c(1,2,3,4,1,2,3,2,2,2,2,1,1,1,1,6,7),
  id = c("a","a","a","a","a", 
         "b","b","b","b","b",
         "c","c","c","c","c",
         "d","d"))

How can this be done?

Solution

  • A possible solution:

    library(dplyr)

df <- data.frame(
  A = c(1,2,3,4,1,2,3,2,2,2,2,1,1,1,1,6,7)
)

df %>% 
  mutate(id = rep(letters, each=5)[1:n()])

#>    A id
#> 1  1  a
#> 2  2  a
#> 3  3  a
#> 4  4  a
#> 5  1  a
#> 6  2  b
#> 7  3  b
#> 8  2  b
#> 9  2  b
#> 10 2  b
#> 11 2  c
#> 12 1  c
#> 13 1  c
#> 14 1  c
#> 15 1  c
#> 16 6  d
#> 17 7  d