These helpers take two endpoints and return the sequence of all
integers within that interval. For seq2_along(), the upper
endpoint is taken from the length of a vector. Unlike
base::seq(), they return an empty vector if the starting point is
a larger integer than the end point.
Examples
seq2(2, 10)
#> [1]  2  3  4  5  6  7  8  9 10
seq2(10, 2)
#> integer(0)
seq(10, 2)
#> [1] 10  9  8  7  6  5  4  3  2
seq2_along(10, letters)
#>  [1] 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
