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.
Let V be any vector space over some field F. Every vector space must contain at least one element: the zero vector 0. Note that if V = { 0 }, then the empty set is a basis for V. Now we consider the case where V contains at least one nonzero element, say v. Define the set X as all linear independent subsets of V.