Median of an array of numbers in JavaScript

The median is the middle value of a sorted numeric array. If the array length is even, the median is the average of the two middle values.

Sort the array in ascending order.
If the array length is odd, pick the middle element.
If the array length is even, average the two middle elements.
Used in statistics to represent the central tendency of data.

JavaScript

function median(arr) {
    var sorted = arr.sort(function (a, b) {
        return a - b;
    });

    var length = sorted.length;

    if (length % 2 === 1) {
        return sorted[(length / 2) - 0.5];
    } else {
        return (sorted[length / 2] + sorted[(length / 2) - 1]) / 2;
    }
}

var arr = [1, 4, 7, 9];
console.log(median(arr));

Output

5.5

[Approach 1]: This approach calculates the median by first identifying the middle index, sorting the array without mutating the original data, and then handling even and odd length cases accordingly.

Calculate a common middle index.
Sort the array without mutation.
Return the middle element (odd) or the average of two middle elements (even).

JavaScript

function median(arr) {
    const middle = (arr.length + 1) / 2;

    // Avoid mutating when sorting
    const sorted = [...arr].sort((a, b) => a - b);
    const isEven = sorted.length % 2 === 0;

    return isEven
        ? (sorted[middle - 1.5] + sorted[middle - 0.5]) / 2
        : sorted[middle - 1];
}

var arr = [1, 4, 7, 9];
console.log(median(arr));

Output

5.5

[Approach 2]: This method finds the median by sorting the array and handling even and odd lengths differently.

Sort the array in ascending order using array slicing to avoid mutation.
Return the middle element for odd lengths or the average of the two middle elements for even lengths.

JavaScript

function median(arr) {
    
    // Sort the array
    arr.sort((a, b) => a - b);

    const length = arr.length;
    const middle = Math.floor(length / 2);

    // Check if the array length is even or odd
    if (length % 2 === 0) {
       
        // If even, return the average of middle two elements
        return (arr[middle - 1] + arr[middle]) / 2;
    } else {
        
        // If odd, return the middle element
        return arr[middle];
    }
}

const arr1 = [1, 4, 7, 9];
console.log(median(arr1)); 

const arr2 = [5, 3, 1, 8, 90];
console.log(median(arr2));

Output

5.5
5

Median of an array of numbers in JavaScript

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