crowding js

crowding.js

const {min, max} = require('underscore')
const first = (arr) => arr[0]
const last = (arr) => arr[arr.length - 1]
const almostZero = (a) => (a > -0.000001 && a < 0.000001)
const almostEqual = (a, b) => almostZero(Math.abs(a) - Math.abs(b))
const population = [
  { objectives: [0.1, 0.2, 0.3] },
  { objectives: [0.2, 0.4, 0.6] },
  { objectives: [0.1, 0.05, 0.3] }
]

function calculateCrowdingDistance(pop) {

  pop.forEach(p => p['dist'] = 0.0)

  const objectivesNumber = pop[0].objectives.length

  for(let i = 1; i < objectivesNumber - 1; i++) {

    const comparable = (p, index) => {
      const next = pop[index + 1]
      if (!next) return 0;
      if (p.objectives[i] < next.objectives[i]) return 1
      if (p.objectives[i] > next.objectives[i]) return -1
      if (almostEqual(p.objectives[i], next.objectives[i])) return 0
    }

    let minVal = min(pop, comparable)
    let maxVal = max(pop, comparable)
    let rge = maxVal.objectives[i] - minVal.objectives[i]

    first(pop).dist = Number.POSITIVE_INFINITY
    last(pop).dist = Number.NEGATIVE_INFINITY

    if (almostZero(rge)) return;

    for(let j = 1; j < pop.length - 1; j++) {
      pop[j].dist += (pop[j + 1].objectives[i] - pop[j - 1].objectives[i])/rge
    }
  }
}

calculateCrowdingDistance(population)
console.log('=========== RESULT ===========')
console.log(population)
console.log('===============================')