JavaScript program to find range average in array

Given an array of numbers and a range, the goal is to calculate the average of all numbers in the range. This problem can be solved in many ways, but in this tutorial we will explore a simple yet effective solution using JavaScript. We'll first define the problem in more detail, including an example of how the function should work. We'll then break down the solution step-by-step, with clear explanations and code snippets. By the end of this tutorial, you will have an in-depth understanding of how to write a JavaScript program that calculates the average of a range in an array. So let’s get started!

Before we begin, let’s define what “average” means. In mathematics, the average (also called the mean) is calculated by adding all the values ​​in a set of numbers and then dividing the sum by the number of values. In the context of an array, the mean of a range of values ​​is the average of all values ​​in the range.

Problem Statement

Given an array of numbers and a range of two numbers, the goal is to calculate the average of all numbers in the range. The range is inclusive, meaning it should include the first and last number in the range. The function should take as input an array and a range and output the average of the numbers in the range. If the input array is empty, the function should return null. The function should also return null if the range is invalid (i.e. the first number is greater than the second number). The output should be a floating point number with two decimal places.

Let us understand this with some examples -

Example 1

Input: Array: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
   Range: [3, 7]
Output: Mean of range [3, 4, 5, 6, 7] is 5.00

In example 1, we have an array of numbers [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] and a range [3, 7]. The average of the range [3, 4, 5, 6, 7] is 5.00, so the output should be 5.00.

Example 2

Input: Array: [2, 4, 6, 8, 10, 12]
   Range: [1, 5]
Output: Mean of range [2, 4, 6, 8, 10] is 6.00

In example 2, we have an array of numbers [2, 4, 6, 8, 10, 12] and the range [1, 5]. The average of the range [2, 4, 6, 8, 10] is 6.00, so the output should be 6.00.

Example 3

Input: Array: [3, 5, 7, 9, 11, 13]
   Range: [7, 3]
Output: null

In example 3, the range [7, 3] is invalid because the first number is greater than the second number, so the output should be null.

Example 4

Input: Array: []
   Range: [1, 5]
Output: null

In example 4, the input array is empty, so the output should also be empty.

Now let us understand the algorithm for the above problem statement.

algorithm

Step 1 - Define function "meanInRange" which takes two parameters: array "arr" and range "range".

Step 2 - Check if the length of the input array "arr" is zero. If so, returns null.

Step 3 - Destructure the "range" array range into two variables "start" and "end".

Step 4 - Check if the value of "start" is greater than "end". If so, returns null.

Step 5 - Use the "slice" method to extract a subarray from the input array "arr" that contains only elements between the start index and the end index of the given range.

Step 6 - Calculate the sum of all elements in the subarray using the "reduce" method.

Step 7 - Divide the sum by the length of the subarray to get the average.

Step 8 - Returns the average as a string formatted to two decimal places, along with a message indicating the range of values ​​used to calculate the average.

Step 9 - End the function.

Now let us understand this algorithm through an example of implementing it using JavaScript.

Example

In this implementation, we define a function "meanInRange" that accepts the array "arr" and the range "range" as input. The function first checks if the input array is empty or if the range is invalid, and returns null if either condition is true. Otherwise, it slices the input array to get the range, uses "reduce" to calculate the sum of the numbers in the range, and calculates the average. Finally, the function logs the average, rounded to two decimal places, to the console using "console.log".

We then call the "meanInRange" function with different input arrays and ranges to test its functionality and print the output to the console.

function meanInRange(arr, range) {
   if (arr.length === 0) {
      return null; // return null if the input array is empty
   }
   const [start, end] = range;
   if (start > end) {
      return null; // return null if the range is invalid
   }
   const rangeArr = arr.slice(start - 1, end); // slice the array to get the range
   const sum = rangeArr.reduce((acc, num) => acc + num, 0); // calculate the sum
   const mean = sum / rangeArr.length; // calculate the mean
   // return the mean rounded to two decimal places
   return `Mean of range [${rangeArr}] is ${mean.toFixed(2)}`;
}
// Example usage:
console.log(meanInRange([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [3, 7])); // should output "Mean of range [3,4,5,6,7] is 5.00"
console.log(meanInRange([2, 4, 6, 8, 10, 12], [1, 5])); // should output "Mean of range [2,4,6,8,10] is 6.00"
console.log(meanInRange([3, 5, 7, 9, 11, 13], [7, 3])); // should output "null"
console.log(meanInRange([], [1, 5])); // should output "null"

in conclusion

In this tutorial, we explored how to find the average of a series of values ​​in an array using JavaScript. We discuss the problem statement and provide algorithms and JavaScript programs that solve the problem. We also learned several usage examples and how to handle edge cases such as empty arrays or invalid ranges. By following this approach, you can easily calculate the average of a series of values ​​within an array in a JavaScript program.

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