JavaScript: Get the standard deviation of an array of numbers

JavaScript fundamental (ES6 Syntax): Exercise-225 with Solution

Standard Deviation

Write a JavaScript program to get the standard deviation of an array of numbers.

• Use Array.prototype.reduce() to calculate the mean, variance and the sum of the variance of the values and determine the standard deviation.
• Omit the second argument, usePopulation, to get the sample standard deviation or set it to true to get the population standard deviation.

Sample Solution:

JavaScript Code:

 // Define a function 'standardDeviation' to calculate the standard deviation of an array
const standardDeviation = (arr, usePopulation = false) => {
  // Calculate the mean of the array
  const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
  
  // Calculate the sum of squared differences from the mean
  const sumOfSquaredDifferences = arr.reduce((acc, val) => acc.concat((val - mean) ** 2), [])
                                      .reduce((acc, val) => acc + val, 0);
  
  // Calculate the standard deviation
  return Math.sqrt(sumOfSquaredDifferences / (arr.length - (usePopulation ? 0 : 1)));
};

// Log the standard deviation of the array with and without using population adjustment
console.log(standardDeviation([10, 2, 38, 23, 38, 23, 21]));  
console.log(standardDeviation([10, 2, 38, 23, 38, 23, 21], true));  

Output:

13.284434142114991
12.29899614287479

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-225-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that computes the standard deviation of an array of numbers using statistical formulas.
• Write a JavaScript function that calculates the variance and then the standard deviation of a dataset.
• Write a JavaScript program that iterates over an array to compute the mean and standard deviation with a single pass algorithm.
• Write a JavaScript function that returns both the standard deviation and variance of an input array.

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