While editing the maps, you may notice that some of the roads are not labeled properly. This means, the road type might be wrong (a highway is marked as a street) or that one road has a few road types (a highway is marked as Freeway, highway and primary at different segments). The importance of proper labeling is in two aspects:
Other sites. R 101: The Subset Function. The subset function is available in base R and can be used to return subsets of a vector, martix, or data frame which meet a particular condition. In my three years of using R, I have repeatedly used the subset() function and believe that it is the most useful tool for selecting elements of a data structure.
1 A set is a subset of another set when all the elements in the first set are also a member of the second set. 2  Given sets and, is a subset of, notated as, if and only if for all, implies. 3  All sets are subsets of the universe. If A and B are two sets, then difference of A and B is the set A-B consisting of all the elements which are elements of A but are not elements of B. 2  Complement of a set A, written as A' or A C is the set consisting of all the elements of which do not belong to A. 3  Thus A' = {x | x and xA}.