seq2: Increasing sequence of integers in an interval

Description

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.

Usage

seq2(from, to)

seq2_along(from, x)

Value

An integer vector containing a strictly increasing
sequence.