#HowToThing #006 — Clustering data using https://thi.ng/k-means, using customizable distance functions and centroid strategies

006.ts

import { HAVERSINE_LATLON } from "@thi.ng/distance";
import { kmeans, meansLatLon } from "@thi.ng/k-means";

// 20 world cities, sorted alphabetically
// data sourced from:
// https://github.com/OpenDataFormats/worldcities/blob/master/src/data/cities.json
const cities = [
    { id: "anchorage", latlon: [61.21806, -149.90028] },
    { id: "berlin", latlon: [52.52437, 13.41053] },
    { id: "boston", latlon: [42.35843, -71.05977] },
    { id: "calgary", latlon: [51.05011, -114.08529] },
    { id: "cape town", latlon: [-33.92584, 18.42322] },
    { id: "detroit", latlon: [42.33143, -83.04575] },
    { id: "harare", latlon: [-17.82772, 31.05337] },
    { id: "london", latlon: [51.50853, -0.12574] },
    { id: "manila", latlon: [14.6042, 120.9822] },
    { id: "nairobi", latlon: [-1.28333, 36.81667] },
    { id: "new york", latlon: [40.71427, -74.00597] },
    { id: "paris", latlon: [48.85341, 2.3488] },
    { id: "philadelphia", latlon: [39.95233, -75.16379] },
    { id: "portland", latlon: [45.52345, -122.67621] },
    { id: "seoul", latlon: [37.566, 126.9784] },
    { id: "shanghai", latlon: [31.22222, 121.45806] },
    { id: "tokyo", latlon: [35.6895, 139.69171] },
    { id: "vancouver", latlon: [49.24966, -123.11934] },
    { id: "vienna", latlon: [48.20849, 16.37208] },
    { id: "windhoek", latlon: [-22.55941, 17.08323] },
];

// cluster based on lat/lon
// IMPORTANT: k-means is a non-deterministic algorithm
const clusters = kmeans(
    // desired number of clusters
    5,
    // item positions
    cities.map((x) => x.latlon),
    // configuration options
    // see:
    {
        // custom centroid calculation for geo locations
        // https://docs.thi.ng/umbrella/k-means/functions/meansLatLon.html
        strategy: meansLatLon,
        // custom distance function for geo location (default: DIST_SQ)
        // using Haversine distance
        // https://docs.thi.ng/umbrella/vectors/functions/distHaversineLatLon.html
        dist: HAVERSINE_LATLON,
    }
);

// print each cluster
for (let c of clusters) {
    console.log(c.items.map((i) => cities[i].id));
}

// [ 'manila', 'seoul', 'shanghai', 'tokyo' ]
// [ 'berlin', 'london', 'paris', 'vienna' ]
// [ 'boston', 'detroit', 'new york', 'philadelphia' ]
// [ 'cape town', 'harare', 'nairobi', 'windhoek' ]
// [ 'anchorage', 'calgary', 'portland', 'vancouver' ]