Following the 2015 Portuguese legislative elections, a comparison between actual seat allocation and simulations of nationwide (i.e. ignoring electoral districts) application of d'Hondt and Sainte-Laguë methods.

voting-systems.js

/**
 * Following the 2015 Portuguese legislative elections, a comparison between
 * actual seat allocation and simulations of nationwide (i.e. ignoring
 * electoral districts) application of d'Hondt and Sainte-Laguë methods.
 *
 * The last three column reflect parliamentary seat assignments.
 *
 *   - "Atribuídos" are the actual seats that were assigned following the
 *   elections
 *
 *   - "Sob d'Hondt" are the seats that would have been assigned if the
 *   electoral system abandoned electoral districts in favor of nationwide
 *   assignment.
 *
 *   - "Sob Sainte-Laguë" are the seats that would have been assigned by
 *   abandoning districts and switching to the Sainte-Laguë assignment 
 *
 *
 *     Partido         Votos    Atribuídos  Sob d'Hondt  Sob Sainte-Laguë
 *     --------------  -------  ----------  -----------  ----------------
 *     PPD/PSD.CDS-PP  1979132  99          90           86
 *     PS              1740280  85          79           75
 *     BE              549153   19          24           24
 *     PCP-PEV         444319   17          20           19
 *     PPD/PSD         81054    5           3            4
 *     PAN             74656    1           3            3
 *     PDR             60912    0           2            3
 *     PCTP/MRPP       59812    0           2            3
 *     L/TDA           38958    0           1            2
 *     PNR             27104    0           1            1
 *     MPT             22384    0           1            1
 *     PTP-MAS         20690    0           0            1
 *     NC              18695    0           0            1
 *     PPM             14799    0           0            1
 *     JPP             14196    0           0            1
 *     PURP            13739    0           0            1
 *     CDS-PP          7536     0           0            0
 *     CDS-PP.PPM      3654     0           0            0
 *     PPV/CDC         2658     0           0            0
 *     PTP             1748     0           0            0
 *
 *
 * The source-code that generated the table follows.
 */

import R from 'ramda';
import Table from 'easy-table';

// data Party = (Number, Number)
//
// A Party is a pair of:
// - number of votes
// - number of allocated seats

// quotSainteLague :: Party -> Number
const quotSainteLague = ([v, s]) => v / (2 * s + 1);

// quotDHondt :: Party -> Number
const quotDHondt = ([v, s]) => v / (s + 1);

// compareAssignments :: Number -> [Number] -> [(Number, Number, Number)]
const compareAssignments = (maxSeats, votes) =>
	R.zipWith(
		(a, b) => [a[0], a[1], b[1]],
		assignSeats(quotSainteLague, maxSeats, votes),
		assignSeats(quotDHondt, maxSeats, votes)
	);

// assignSeats :: Function -> Number -> [Number] -> [Party]
const assignSeats = (quot, maxSeats, votes) =>
	R.repeat(null, maxSeats).reduce(nextRound(quot), votes.map(v => [v, 0]));

// nextRound :: Function -> [Party] -> [Party]
const nextRound = R.curry((quot, ps) => {
	const i = nextWinner(quot, ps);
	const p = [ ps[i][0], ps[i][1] + 1 ];
	return replaceAtIndex(i, p, ps);
});

// nextWinner :: Function -> [Party] -> Number
const nextWinner = (quot, ps) => indexOfMax(ps.map(quot));

// indexOfMax :: [Number] -> Number
const indexOfMax = R.converge(R.indexOf, R.apply(Math.max), R.identity);

// replaceAtIndex :: Number -> a -> [a] -> [a]
const replaceAtIndex = (index, x, xs) =>
	[ ...xs.slice(0, index), x, ...xs.slice(index + 1) ];

const compare2015 = () => {
	const seats = 226;
	const votes = [
		[ 1979132, 'PPD/PSD.CDS-PP', 99 ],
		[ 1740280, 'PS', 85 ],
		[ 549153, 'BE', 19 ],
		[ 444319, 'PCP-PEV', 17 ],
		[ 81054, 'PPD/PSD', 5 ],
		[ 74656, 'PAN', 1 ],
		[ 60912, 'PDR', 0 ],
		[ 59812, 'PCTP/MRPP', 0 ],
		[ 38958, 'L/TDA', 0 ],
		[ 27104, 'PNR', 0 ],
		[ 22384, 'MPT', 0 ],
		[ 20690, 'PTP-MAS', 0 ],
		[ 18695, 'NC', 0 ],
		[ 14799, 'PPM', 0 ],
		[ 14196, 'JPP', 0 ],
		[ 13739, 'PURP', 0 ],
		[ 7536, 'CDS-PP', 0 ],
		[ 3654, 'CDS-PP.PPM', 0 ],
		[ 2658, 'PPV/CDC', 0 ],
		[ 1748, 'PTP', 0 ],
	];

	console.log(Table.print(
		compareAssignments(seats, votes.map(R.nth(0)))
			.map((line, i) => ({
				'Partido': votes[i][1],
				'Votos': line[0],
				'Atribuídos': votes[i][2],
				'Sob d\'Hondt': line[2],
				'Sob Sainte-Laguë': line[1],
			}))
	));
};

compare2015();