redist.segcalc: Segregation index calculation for MCMC redistricting.

In redist: Simulation Methods for Legislative Redistricting

Segregation index calculation for MCMC redistricting.

Description

redist.segcalc calculates the dissimilarity index of segregation (see Massey & Denton 1987 for more details) for a specified subgroup under any redistricting plan.

Usage

segregation_index(
  map,
  group_pop,
  total_pop = map[[attr(map, "pop_col")]],
  .data = cur_plans()
)

redist.segcalc(plans, group_pop, total_pop)

Arguments

map	a redist_map object
group_pop	A vector of populations for some subgroup of interest.
total_pop	A vector containing the populations of each geographic unit.
.data	a redist_plans object
plans	A matrix of congressional district assignments or a redist object.

Value

redist.segcalc returns a vector where each entry is the dissimilarity index of segregation (Massey & Denton 1987) for each redistricting plan in algout.

References

Fifield, Benjamin, Michael Higgins, Kosuke Imai and Alexander Tarr. (2016) "A New Automated Redistricting Simulator Using Markov Chain Monte Carlo." Working Paper. Available at http://imai.princeton.edu/research/files/redist.pdf.

Massey, Douglas and Nancy Denton. (1987) "The Dimensions of Social Segregation". Social Forces.

Examples

data(fl25)
data(fl25_enum)
data(fl25_adj)

## Get an initial partition
init_plan <- fl25_enum$plans[, 5118]
fl25$init_plan <- init_plan

## 25 precinct, three districts - no pop constraint ##
fl_map <- redist_map(fl25, existing_plan = 'init_plan', adj = fl25_adj)
alg_253 <- redist_flip(fl_map, nsims = 10000)


## Get Republican Dissimilarity Index from simulations
# old: rep_dmi_253 <- redist.segcalc(alg_253, fl25$mccain, fl25$pop)
rep_dmi_253 <- seg_dissim(alg_253, fl25, mccain, pop)  |>
    redistmetrics::by_plan(ndists = 3)

redist documentation built on Aug. 8, 2025, 7:44 p.m.