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Theory
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Median of an even number of elements

Well done! Take a patty from the shelf.
But there are two of them there.
Take the one in the middle.

Approximately the same situation occurs with calculating the median when an even number of elements are stored in the array. But unlike the situation with patties, we found the solution for the median. If the number of elements is even, the median is calculated as the average of the two elements: the left one and the right one from the middle.

// Median: 3
[0, 1, 2, 4, 50, 100]

Let’s once again derive the formulas of the indices of the two elements: the left one and the right one from the middle.

// Length 1, left index 1, right index 2
[1, 2, 3, 4]

// Length 6, left index 2, right index 3
[1, 2, 3, 4, 5, 6]

// Length 8, left index 3, right index 4
[1, 2, 3, 4, 5, 6, 7, 8]

Divide the array length by two and subtract one: and we got the left index. Divide array length by two: and we got the right index.

Let’s add calculating the median for an even number of elements in the array to the alternative branch of the condition.

Please note, that this median search algorithm will not work for empty arrays and the result will be NaN. It’s because value undefined sneaks into the calculations, and this value returns NaN in any mathematical operations.

script.js

JavaScript

var usersByDay = [1, 2, 3, 4, 5, 6]; console.log(usersByDay); if (usersByDay.length % 2 !== 0) { var medianIndex = (usersByDay.length - 1) / 2; console.log(medianIndex); var median = usersByDay[medianIndex]; console.log(median); }

Goalscompleted

In the alternative branch of the condition, add the variable leftIndex with the value usersByDay.length / 2 - 1.
And variable rightIndex with value usersByDay.length / 2.
Log both variables in the console.
In the same condition branch, add variable median with value (usersByDay[leftIndex] + usersByDay[rightIndex]) / 2.
Log it in the console as well.

Median of an even number of elements

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