covutils/lib/array.js

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.minMax = minMax;
exports.indicesOfNearest = indicesOfNearest;
exports.indexOfNearest = indexOfNearest;
function minMax(arr) {
  var len = arr.length;
  var min = Infinity;
  var max = -Infinity;
  while (len--) {
    var el = arr[len];
    if (el == null) {
      // do nothing
    } else if (el < min) {
        min = el;
      } else if (el > max) {
        max = el;
      }
  }
  if (min === Infinity) {
    min = max;
  } else if (max === -Infinity) {
    max = min;
  }
  if (min === Infinity || min === -Infinity) {
    // all values were null
    min = null;
    max = null;
  }
  return [min, max];
}

/**
 * Return the indices of the two neighbors in the sorted array closest to the given number.
 *
 * @example
 * var a = [2,5,8,12,13]
 * var i = CovUtils.indicesOfNearest(a, 6)
 * // i == [1,2]
 * var j = CovUtils.indicesOfNearest(a, 5)
 * // j == [1,1]
 * var k = CovUtils.indicesOfNearest(a, 50)
 * // k == [4,4]
 *
 * @param {Array<number>} a The array to search through. Must be sorted, ascending or descending.
 * @param {number} x The target number.
 * @return {[lo,hi]} The indices of the two closest values, may be equal.
 *   If `x` exists in the array, both neighbors point to `x`.
 *   If `x` is lower (greater if descending) than the first value, both neighbors point to 0.
 *   If `x` is greater (lower if descending) than the last value, both neighbors point to the last index.
 */
function indicesOfNearest(a, x) {
  if (a.length === 0) {
    throw new Error('Array must have at least one element');
  }
  var lo = -1;
  var hi = a.length;
  var ascending = a.length === 1 || a[0] < a[1];
  // we have two separate code paths to help the runtime optimize the loop
  if (ascending) {
    while (hi - lo > 1) {
      var mid = Math.round((lo + hi) / 2);
      if (a[mid] <= x) {
        lo = mid;
      } else {
        hi = mid;
      }
    }
  } else {
    while (hi - lo > 1) {
      var _mid = Math.round((lo + hi) / 2);
      if (a[_mid] >= x) {
        // here's the difference
        lo = _mid;
      } else {
        hi = _mid;
      }
    }
  }
  if (a[lo] === x) hi = lo;
  if (lo === -1) lo = hi;
  if (hi === a.length) hi = lo;
  return [lo, hi];
}

/**
 * Return the index of the value closest to the given number in a sorted array.
 *
 * @example
 * var a = [2,5,8,12,13]
 * var i = CovUtils.indexOfNearest(a, 6)
 * // i == 1
 * var j = CovUtils.indexOfNearest(a, 7)
 * // j == 2
 * var k = CovUtils.indexOfNearest(a, 50)
 * // k == 4
 *
 * @param {Array<number>} a The array to search through. Must be sorted, ascending or descending.
 * @param {number} x The target number.
 * @return {number} The array index whose value is closest to `x`.
 *   If `x` happens to be exactly between two values, then the lower index is returned.
 */
function indexOfNearest(a, x) {
  var i = indicesOfNearest(a, x);
  var lo = i[0];
  var hi = i[1];
  if (Math.abs(x - a[lo]) <= Math.abs(x - a[hi])) {
    return lo;
  } else {
    return hi;
  }
}