@ai-on-browser/data-analysis-models/lib/model/fastmap.js

Data analysis model package without any dependencies

/**
 * FastMap
 */
export default class FastMap {
	// http://ibisforest.org/index.php?FastMap
	/**
	 * @param {number} rd Reduced dimension
	 */
	constructor(rd) {
		this._rd = rd
	}

	/**
	 * Returns reduced values.
	 * @param {Array<Array<number>>} x Training data
	 * @returns {Array<Array<number>>} Predicted values
	 */
	predict(x) {
		const d = []
		const n = x.length
		const m = x[0].length
		for (let i = 0; i < n; d[i++] = []);
		for (let i = 0; i < n; i++) {
			d[i][i] = 0
			for (let j = i + 1; j < n; j++) {
				let ds = 0
				for (let k = 0; k < m; k++) {
					ds += (x[i][k] - x[j][k]) ** 2
				}
				d[i][j] = d[j][i] = Math.sqrt(ds)
			}
		}

		const argmax = arr => {
			let idx = -1
			let val = -Infinity
			for (let i = 0; i < arr.length; i++) {
				if (val < arr[i]) {
					val = arr[i]
					idx = i
				}
			}
			return idx
		}

		const y = []
		for (let i = 0; i < n; y[i++] = []);
		for (let k = 0; k < this._rd; k++) {
			const p = Math.floor(Math.random() * n)
			const a = argmax(d[p])
			const b = argmax(d[a])

			for (let i = 0; i < n; i++) {
				y[i][k] = (d[a][i] ** 2 + d[a][b] ** 2 - d[b][i] ** 2) / (2 * d[a][b])
			}

			for (let i = 0; i < n; i++) {
				for (let j = i + 1; j < n; j++) {
					d[i][j] = d[j][i] = Math.sqrt(d[i][j] ** 2 - (y[i][k] - y[j][k]) ** 2)
				}
			}
		}
		return y
	}
}