source: node_modules/d3-scale/src/quantile.js@ e4c61dd

import {ascending, bisect, quantileSorted as threshold} from "d3-array";
import {initRange} from "./init.js";

export default function quantile() {
  var domain = [],
      range = [],
      thresholds = [],
      unknown;

  function rescale() {
    var i = 0, n = Math.max(1, range.length);
    thresholds = new Array(n - 1);
    while (++i < n) thresholds[i - 1] = threshold(domain, i / n);
    return scale;
  }

  function scale(x) {
    return x == null || isNaN(x = +x) ? unknown : range[bisect(thresholds, x)];
  }

  scale.invertExtent = function(y) {
    var i = range.indexOf(y);
    return i < 0 ? [NaN, NaN] : [
      i > 0 ? thresholds[i - 1] : domain[0],
      i < thresholds.length ? thresholds[i] : domain[domain.length - 1]
    ];
  };

  scale.domain = function(_) {
    if (!arguments.length) return domain.slice();
    domain = [];
    for (let d of _) if (d != null && !isNaN(d = +d)) domain.push(d);
    domain.sort(ascending);
    return rescale();
  };

  scale.range = function(_) {
    return arguments.length ? (range = Array.from(_), rescale()) : range.slice();
  };

  scale.unknown = function(_) {
    return arguments.length ? (unknown = _, scale) : unknown;
  };

  scale.quantiles = function() {
    return thresholds.slice();
  };

  scale.copy = function() {
    return quantile()
        .domain(domain)
        .range(range)
        .unknown(unknown);
  };

  return initRange.apply(scale, arguments);
}