quantize.js

import {bisect} from "d3-array";
import {linearish} from "./linear.js";
import {initRange} from "./init.js";

export default function quantize() {
  var x0 = 0,
      x1 = 1,
      n = 1,
      domain = [0.5],
      range = [0, 1],
      unknown;

  function scale(x) {
    return x != null && x <= x ? range[bisect(domain, x, 0, n)] : unknown;
  }

  function rescale() {
    var i = -1;
    domain = new Array(n);
    while (++i < n) domain[i] = ((i + 1) * x1 - (i - n) * x0) / (n + 1);
    return scale;
  }

  scale.domain = function(_) {
    return arguments.length ? ([x0, x1] = _, x0 = +x0, x1 = +x1, rescale()) : [x0, x1];
  };

  scale.range = function(_) {
    return arguments.length ? (n = (range = Array.from(_)).length - 1, rescale()) : range.slice();
  };

  scale.invertExtent = function(y) {
    var i = range.indexOf(y);
    return i < 0 ? [NaN, NaN]
        : i < 1 ? [x0, domain[0]]
        : i >= n ? [domain[n - 1], x1]
        : [domain[i - 1], domain[i]];
  };

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

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

  scale.copy = function() {
    return quantize()
        .domain([x0, x1])
        .range(range)
        .unknown(unknown);
  };

  return initRange.apply(linearish(scale), arguments);
}