redist (version 1.1)

redist.rsg: Redistricting via Random Seed and Grow Algorithm

Description

redist.rsg generates redistricting plans using a random seed a grow algorithm. This is the non-compact districting algorithm described in Chen and Rodden (2013). The algorithm can provide start values for the other redistricting routines in this package.

Usage

redist.rsg(adj.list, population, ndists, thresh, verbose = TRUE, maxiter=5000)

Arguments

adj.list

list of length N, where N is the number of precincts. Each list element is an integer vector indicating which precincts that precinct is adjacent to. It is assumed that precinct numbers start at 0.

population

numeric vector of list N, where N is the number of precincts. Each element lists the population total of the corresponding precinct, and is used to enforce population constraints.

ndists

integer, the number of districts we want to partition the precincts into.

thresh

numeric, indicating how close district population targets have to be to the target population before algorithm converges. thresh=0.05 for example means that all districts must be between 0.95 and 1.05 times the size of target.pop in population si

verbose

boolean, indicating whether the time to run the algorithm is printed.

maxiter

integer, indicating maximum number of iterations to attempt before convergence to population constraint fails. If it fails once, it will use a different set of start values and try again. If it fails again, redist.rsg() returns an object of all

Value

• list, containing three objects containing the completed redistricting plan.
  • district_membership
  { A vector of length N, indicating the district membership of each precinct.}
• district_list
  A list of length Ndistrict. Each list contains a vector of the precincts in the respective district.
• district_pop
  A vector of length Ndistrict, containing the population totals of the respective districts.

References

Jowei Chen and Jonathan Rodden (2013) ``Unintentional Gerrymandering: Political Geography and Electoral Bias in Legislatures.'' Quarterly Journal of Political Science. 8(3): 239-269.

Examples

### Real data example from test set

data("algdat.pfull")
res <- redist.rsg(algdat.pfull$adjlist, algdat.pfull$precinct.data$pop, 3, 0.05)


### Example that generates test data from a square map with equal population districts
### Number of precincts is Nrows*Ncols
### getTest() outputs an adjacency list out of specified rows and columns

genTest <- function(Nrows,Ncols){

NN <- Nrows * Ncols

geog <- matrix(NA,nrow=Nrows+2, ncol=Ncols+2)
geog[2:(Nrows+1), 2:(Ncols+1)] <- 0:(NN-1)

adj.list <- vector("list", NN)

for(i in 2:(Nrows+1)){
	for(j in 2:(Ncols+1)){
		adj.list[[ geog[i,j] + 1 ]] <- c(geog[i-1,j],geog[i+1,j],geog[i,j-1],geog[i,j+1])
	}
}
adj.list <- lapply(adj.list, na.omit)
adj.list <- lapply(adj.list, as.numeric)
return(adj.list)
}

### Generate a 100x100 precinct map and redistrict it into 10 districts
adj.list <- genTest(100,100)
population <- rep(300,length(adj.list))
tmp <- redist.rsg(adj.list, population, 10, 0.05)