histogram.js

import {slice} from "./array";
import bisect from "./bisect";
import constant from "./constant";
import extent from "./extent";
import identity from "./identity";
import range from "./range";
import {tickStep} from "./ticks";
import sturges from "./threshold/sturges";

export default function() {
  var value = identity,
      domain = extent,
      threshold = sturges;

  function histogram(data) {
    var i,
        n = data.length,
        x,
        values = new Array(n);

    for (i = 0; i < n; ++i) {
      values[i] = value(data[i], i, data);
    }

    var xz = domain(values),
        x0 = xz[0],
        x1 = xz[1],
        tz = threshold(values, x0, x1);

    // Convert number of thresholds into uniform thresholds.
    if (!Array.isArray(tz)) {
      tz = tickStep(x0, x1, tz);
      tz = range(Math.ceil(x0 / tz) * tz, Math.floor(x1 / tz) * tz, tz); // exclusive
    }

    // Remove any thresholds outside the domain.
    var m = tz.length;
    while (tz[0] <= x0) tz.shift(), --m;
    while (tz[m - 1] > x1) tz.pop(), --m;

    var bins = new Array(m + 1),
        bin;

    // Initialize bins.
    for (i = 0; i <= m; ++i) {
      bin = bins[i] = [];
      bin.x0 = i > 0 ? tz[i - 1] : x0;
      bin.x1 = i < m ? tz[i] : x1;
    }

    // Assign data to bins by value, ignoring any outside the domain.
    for (i = 0; i < n; ++i) {
      x = values[i];
      if (x0 <= x && x <= x1) {
        bins[bisect(tz, x, 0, m)].push(data[i]);
      }
    }

    return bins;
  }

  histogram.value = function(_) {
    return arguments.length ? (value = typeof _ === "function" ? _ : constant(_), histogram) : value;
  };

  histogram.domain = function(_) {
    return arguments.length ? (domain = typeof _ === "function" ? _ : constant([_[0], _[1]]), histogram) : domain;
  };

  histogram.thresholds = function(_) {
    return arguments.length ? (threshold = typeof _ === "function" ? _ : Array.isArray(_) ? constant(slice.call(_)) : constant(_), histogram) : threshold;
  };

  return histogram;
}