Data Science Math Skills

functions.js

// Data Science Math Skills
// https://www.coursera.org/learn/datasciencemathskills/home/welcome

// Sigma summation
function sigma(n, i, f) {
  var sum = 0;
  while (i <= n) {
    sum += f(i++);
  }
  return sum;
}

// sigma(100, 1, i => i);
// => 1050

// Maen value
function mean(x) {
  var n = x.length;
  return 1 / n * sigma(n, 1, function (i) {
    // decrement index by one since array index in
    // JavaScript starts from zero
    return x[i-1];
  });
}

// mean([5, 6, 7]);
// => 6

// Variance population
function variance(x) {
  var n = x.length;
  return 1 / n * sigma(n, 1, function (i) {
    // decrement index by one since array index in
    // JavaScript starts from zero
    var res = x[i-1] - mean(x);
    // square result
    return res * res;
  });
}

// variance([1, 5, 12])
// => 20.666666666666664

// Standart deviation
function deviation(x) {
  return Math.sqrt(variance(x));
}

// deviation([2,4,4,4,5,5,7,9]);
// => 2