Index map regions

Assigns an index to each map region, useful for map coloring.

Usage

match.map(database, regions, exact = FALSE, warn = TRUE)

Author

Tom Minka

Arguments

database

character string naming a geographical database, or a map object. See the documentation for map for more details.

regions

a vector of names, or more generally regular expressions to match against the map region names.

exact

If TRUE, only exact matches with regions are considered. Otherwise each element of regions is assumed to be a regular expression. Matches are always case-insensitive.

warn

If TRUE, a warning is printed when an element of regions matches nothing in the map.

Value

Returns an integer vector giving an index to each region in the database. The index is the index of the string in regions which matches the region name. Matching is done as in map. More specifically, all regions r whose name matches regions[i] will have index i. Unmatched regions will have index NA. Overlapping matches cause an error.

This behavior differs from pmatch because a single entry in regions may match several entries in the map.

See also

grep

References

Richard A. Becker, and Allan R. Wilks, "Maps in S", AT&T Bell Laboratories Statistics Research Report, 1991.

Examples

# filled map showing Republican vote in 1900
# (figure 6 in the reference)
data(state, package = "datasets")
data(votes.repub)
state.to.map <- match.map("state", state.name)
x <- votes.repub[state.to.map, "1900"]
gray.colors <- function(n) gray(rev(0:(n - 1))/n)
color <- gray.colors(100)[floor(x)]
map("state", fill = TRUE, col = color); map("state", add = TRUE)