Mark the first row in each group of rows.

Mark the first row in each group of rows.

mark_first_in_each_group(data, group_cols)

Arguments

data

a data.frame ordered with respect to groups
group_cols

character names of the grouping columns

Value

numeric vector with index of first row in each group

Examples


d <- wrapr::build_frame(
    "g", "v" |
    1  , 1L  |
    0  , 2L  |
    0  , 3L  |
    1  , 4L  |
    1  , 5L  )

d <- d[wrapr::orderv(d), , drop = FALSE]
d$fi <- mark_first_in_each_group(d, "g")

print(d)
#>   g v fi
#> 2 0 2  1
#> 3 0 3  1
#> 1 1 1  3
#> 4 1 4  3
#> 5 1 5  3