Cumulative average of pair of elements in JavaScript

We have an array of numbers and are required to write a function that returns an array with the average of the corresponding element and its predecessor.

For the first element, as there are no predecessors, so that very element should be returned.

Let’s write the code for this function, we will use the Array.prototype.map() function to solve this problem.

Example

The code for this will be −

const arr = [3, 5, 7, 8, 3, 5, 7, 4, 2, 8, 4, 2, 1];
const consecutiveAverage = arr => {
   return arr.map((el, ind, array) => {
      const first = (array[ind-1] || 0);
      const second = (1 + !!ind);
      return ((el + first) / second);
   });
};
console.log(consecutiveAverage(arr));

Output

The output in the console will be −

[
   3, 4, 6, 7.5, 5.5, 4,
   6, 5.5, 3, 5, 6, 3,
   1.5
]