below-median.js

var count = require('lodash.countby');
var sum = require('lodash.sum');
var filter = require('lodash.filter');
var size = require('lodash.size');
var values = require('lodash.values');
var pairs = require('lodash.pairs');
var head = require('lodash.head');
var assign = require('lodash.assign');
var mapToObject = require('@quarterto/map-to-object');

module.exports = (xs, ensure = []) => {
  const zeroes = mapToObject(ensure, () => 0);
  const c = assign(zeroes, count(xs));
  const μ = sum(values(c))/size(c);
  return filter(pairs(c), (v) => v[1] <= μ).map(head);
};