I have a data.frame as simple as this one:

id group idu  value
1  1     1_1  34
2  1     2_1  23
3  1     3_1  67
4  2     4_2  6
5  2     5_2  24
6  2     6_2  45
1  3     1_3  34
2  3     2_3  67
3  3     3_3  76

from where I want to retrieve a subset with the first entries of each group; something like:

id group idu value
1  1     1_1 34
4  2     4_2 6
1  3     1_3 34

id is not unique so the approach should not rely on it.

Can I achieve this avoiding loops?

data <- data.frame(
  id = c(1L, 2L, 3L, 4L, 5L, 6L, 1L, 2L, 3L),
  group = rep(1:3, each = 3L),
  idu = factor(c("1_1", "2_1", "3_1", "4_2", "5_2", "6_2", "1_3", "2_3", "3_3")),
  value = c(34L, 23L, 67L, 6L, 24L, 45L, 34L, 67L, 76L)
)
r subset
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