1 | import { containsCollections } from '../../utils/collection'
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2 | import { flatten } from '../../utils/array'
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3 | import { factory } from '../../utils/factory'
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4 | import { improveErrorMessage } from './utils/improveErrorMessage'
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5 |
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6 | const name = 'median'
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7 | const dependencies = ['typed', 'add', 'divide', 'compare', 'partitionSelect']
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8 |
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9 | export const createMedian = /* #__PURE__ */ factory(name, dependencies, ({ typed, add, divide, compare, partitionSelect }) => {
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10 | /**
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11 | * Compute the median of a matrix or a list with values. The values are
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12 | * sorted and the middle value is returned. In case of an even number of
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13 | * values, the average of the two middle values is returned.
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14 | * Supported types of values are: Number, BigNumber, Unit
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15 | *
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16 | * In case of a (multi dimensional) array or matrix, the median of all
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17 | * elements will be calculated.
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18 | *
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19 | * Syntax:
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20 | *
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21 | * math.median(a, b, c, ...)
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22 | * math.median(A)
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23 | *
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24 | * Examples:
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25 | *
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26 | * math.median(5, 2, 7) // returns 5
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27 | * math.median([3, -1, 5, 7]) // returns 4
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28 | *
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29 | * See also:
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30 | *
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31 | * mean, min, max, sum, prod, std, variance, quantileSeq
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32 | *
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33 | * @param {... *} args A single matrix or or multiple scalar values
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34 | * @return {*} The median
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35 | */
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36 | const median = typed(name, {
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37 | // median([a, b, c, d, ...])
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38 | 'Array | Matrix': _median,
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39 |
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40 | // median([a, b, c, d, ...], dim)
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41 | 'Array | Matrix, number | BigNumber': function (array, dim) {
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42 | // TODO: implement median(A, dim)
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43 | throw new Error('median(A, dim) is not yet supported')
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44 | // return reduce(arguments[0], arguments[1], ...)
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45 | },
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46 |
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47 | // median(a, b, c, d, ...)
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48 | '...': function (args) {
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49 | if (containsCollections(args)) {
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50 | throw new TypeError('Scalar values expected in function median')
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51 | }
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52 |
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53 | return _median(args)
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54 | }
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55 | })
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56 |
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57 | /**
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58 | * Recursively calculate the median of an n-dimensional array
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59 | * @param {Array} array
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60 | * @return {Number} median
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61 | * @private
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62 | */
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63 | function _median (array) {
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64 | try {
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65 | array = flatten(array.valueOf())
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66 |
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67 | const num = array.length
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68 | if (num === 0) {
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69 | throw new Error('Cannot calculate median of an empty array')
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70 | }
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71 |
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72 | if (num % 2 === 0) {
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73 | // even: return the average of the two middle values
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74 | const mid = num / 2 - 1
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75 | const right = partitionSelect(array, mid + 1)
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76 |
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77 | // array now partitioned at mid + 1, take max of left part
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78 | let left = array[mid]
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79 | for (let i = 0; i < mid; ++i) {
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80 | if (compare(array[i], left) > 0) {
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81 | left = array[i]
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82 | }
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83 | }
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84 |
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85 | return middle2(left, right)
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86 | } else {
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87 | // odd: return the middle value
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88 | const m = partitionSelect(array, (num - 1) / 2)
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89 |
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90 | return middle(m)
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91 | }
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92 | } catch (err) {
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93 | throw improveErrorMessage(err, 'median')
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94 | }
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95 | }
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96 |
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97 | // helper function to type check the middle value of the array
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98 | const middle = typed({
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99 | 'number | BigNumber | Complex | Unit': function (value) {
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100 | return value
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101 | }
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102 | })
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103 |
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104 | // helper function to type check the two middle value of the array
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105 | const middle2 = typed({
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106 | 'number | BigNumber | Complex | Unit, number | BigNumber | Complex | Unit': function (left, right) {
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107 | return divide(add(left, right), 2)
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108 | }
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109 | })
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110 |
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111 | return median
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112 | })
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