Find the median value in array of numbers

index.js

const assert = require('assert')

// I'm trusting R's built in helper for calculating expected values
// https://repl.it/repls/IroncladLightpinkBookmark
const samples = [
  {
    input: [187],
    expected: 187,
  },
  {
    input: [378, 329, 445],
    expected: 378,
  },
  {
    input: [102, 152, 441, 200, 256, 216, 440, 234, 392, 358, 270, 506],
    expected: 263,
  },
  {
    input: [135, 60, 66, 85, 101, 68, 80],
    expected: 80,
  },
  {
    input: [36, 222, 56, 86, 87, 95],
    expected: 86.5,
  },
  {
    input: [1611, 144, 136, 149, 168, 169, 144, 712, 183, 148, 157, 143],
    expected: 153,
  },
  {
    input: [794,267,404,219],
    expected: 335.5,
  },
  {
    input: [207],
    expected: 207,
  },
  {
    input: [128,218,239,272,277,219,372,208,211,471,319,385,350],
    expected: 272,
  },
  {
    input: [89,80,48,144,437,86,72,99,66],
    expected: 86,
  },
  {
    input: [59,137,99],
    expected: 99,
  },
  {
    input: [73,126,133,110,140,131,141,137,156,174,163],
    expected: 137,
  },
]

for (const sample of samples) {
  const result = findMedian(sample.input)

  assert.equal(result, sample.expected)
}

function findMedian(inputMaybe = []) {
  // Sort in ascending order assuming data sanitized for e.g., `Infinity` and `NaN` values,
  // but get a copy first, because sorting happens in place
  const input = [...inputMaybe].sort((a, b) => a - b)

  // https://en.wikipedia.org/wiki/Median#Finite_data_set_of_numbers
  const i = 0.5 * (input.length + 1)
  const a = Math.floor(i) - 1
  const b = Math.ceil(i) - 1

  return 0.5 * (input[a] + input[b])
}

# Tested with Node.js 12.18.4, clean exit means tests are passing
git clone https://gist.github.com/6f5162b6f115be4778a372f24a5e2502.git find-median
cd find-median
node index.js