Simple clustering

cluster.js

const EPSILON = 0.1

const cluster = (array, threshold) => {
  for (const e of array) {
    return array.filter(e_ => Math.abs(e - e_) < EPSILON).length / array.length >= threshold
  }
}

if (
  cluster([0, 0.0001, 0.01, 0.0, 9], 0.5) &&
  cluster([0, 0.0001, 0.01, 0.0, 9], 0.75) &&
  !cluster([0, 0.0001, 0.01, 0.0, 9], 0.9) &&
  !cluster([0, 0, 0, 1, 1, 1, 1], 0.75) &&
  !cluster([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], 0.2)
) {
  console.log('Success')
} else {
  console.log('Failure')
}