The function uniquemap is generic, with methods
for point patterns, data frames, and a default method.
The default method expects a vector. It determines whether any entries
of the vector x are duplicated,
and constructs a mapping of the indices of x
so that all duplicates are mapped to a unique representative index.
The result is an integer vector u such that
u[j] = i if
the entries x[i] and x[j] are identical and
point i has been chosen as the unique representative.
The entry u[i] = i means either that point i is
unique, or that it has been chosen as the unique representative
of its equivalence class.
The method for data.frame determines whether any rows of the
data frame x are duplicated, and constructs a mapping of the
row indices so that all duplicate rows are mapped to a unique
representative row.