A JavaScript basic implementation of the Benford Law

benford.js

/**
 * A JavaScript basic implementation of the Benford Law
 * @param data an integer array to be used on algorithm
 *   
 * #### Usage
 * const citiesPopulation = [12252023, 6718903, 3015268, …, 765]
 * const benford = new Benford(citiesPopulation)
 * benford.printAsTable()
 */

function Benford(data = []) {
  const benfordProbabilities = {
    1: 0.301,
    2: 0.176,
    3: 0.125,
    4: 0.097,
    5: 0.079,
    6: 0.067,
    7: 0.058,
    8: 0.051,
    9: 0.046
  }
  const initialDigits = {
    1: { count: 0 },
    2: { count: 0 },
    3: { count: 0 },
    4: { count: 0 },
    5: { count: 0 },
    6: { count: 0 },
    7: { count: 0 },
    8: { count: 0 },
    9: { count: 0 }
  }
  function presentDataWithPadding(value, padding = 20) {
    return `${(value * 100).toFixed(1)}%`.padStart(padding, " ")
  }

  const sanitized = data.filter(e => e > 0)
  this.sanitizedInput = {
    data: sanitized,
    size: sanitized.length
  }

  this.digits = sanitized.reduce((acc, number) => {
    const digit = +(`${number}`.charAt(0))
    const count = acc[digit].count + 1
    const percentage = count / sanitized.length
    const deviation = percentage - benfordProbabilities[digit]

    acc[digit] = { count, percentage, deviation }

    return acc
  }, initialDigits)

  this.printAsTable = () => {
    const header =
      " DIGIT │ DIGIT OCCURRENCES (%) │ BENFORD PROBABILITIES (%) │ DEVIATION "
    const divider =
      "───────┼───────────────────────┼───────────────────────────┼───────────"
    const body = Object.entries(this.digits).reduce((
      acc,
      [digit, { percentage, deviation }]
    ) => {
      return acc +
        `${digit}`.padStart(6, " ") + 
        " │ " +
        presentDataWithPadding(percentage, 21) +
        " │ " +
        presentDataWithPadding(benfordProbabilities[digit], 25) +
        " │ " +
        presentDataWithPadding(deviation, 9) +
        "\n"
    }, "")

    const table = [header, divider, body]

    console.log(table.join("\n"))
  }
}