bin.js

import {slice} from "./array.js";
import bisect from "./bisect.js";
import constant from "./constant.js";
import extent from "./extent.js";
import identity from "./identity.js";
import nice from "./nice.js";
import ticks, {tickIncrement} from "./ticks.js";
import sturges from "./threshold/sturges.js";

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

  function histogram(data) {
    if (!Array.isArray(data)) data = Array.from(data);

    var i,
        n = data.length,
        x,
        step,
        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, and nice the
    // default domain accordingly.
    if (!Array.isArray(tz)) {
      const max = x1, tn = +tz;
      if (domain === extent) [x0, x1] = nice(x0, x1, tn);
      tz = ticks(x0, x1, tn);

      // If the domain is aligned with the first tick (which it will by
      // default), then we can use quantization rather than bisection to bin
      // values, which is substantially faster.
      if (tz[0] <= x0) step = tickIncrement(x0, x1, tn);

      // If the last threshold is coincident with the domain’s upper bound, the
      // last bin will be zero-width. If the default domain is used, and this
      // last threshold is coincident with the maximum input value, we can
      // extend the niced upper bound by one tick to ensure uniform bin widths;
      // otherwise, we simply remove the last threshold. Note that we don’t
      // coerce values or the domain to numbers, and thus must be careful to
      // compare order (>=) rather than strict equality (===)!
      if (tz[tz.length - 1] >= x1) {
        if (max >= x1 && domain === extent) {
          const step = tickIncrement(x0, x1, tn);
          if (isFinite(step)) {
            if (step > 0) {
              x1 = (Math.floor(x1 / step) + 1) * step;
            } else if (step < 0) {
              x1 = (Math.ceil(x1 * -step) + 1) / -step;
            }
          }
        } else {
          tz.pop();
        }
      }
    }

    // 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.
    if (isFinite(step)) {
      if (step > 0) {
        for (i = 0; i < n; ++i) {
          if ((x = values[i]) != null && x0 <= x && x <= x1) {
            bins[Math.min(m, Math.floor((x - x0) / step))].push(data[i]);
          }
        }
      } else if (step < 0) {
        for (i = 0; i < n; ++i) {
          if ((x = values[i]) != null && x0 <= x && x <= x1) {
            const j = Math.floor((x0 - x) * step);
            bins[Math.min(m, j + (tz[j] <= x))].push(data[i]); // handle off-by-one due to rounding
          }
        }
      }
    } else {
      for (i = 0; i < n; ++i) {
        if ((x = values[i]) != null && 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;
}