How to calculate the difference of two values that are present in sub arrays of an array with a loop-CodePudding

I have an array of arrays where each sub-array holds two values each. The end goal here is calculate the decrease/increase of each sub-array so I can then calculate an overall average. In this case, I am trying to calculate the average month on month change to then work out a total average for the year.

let groupedMonthTotals = [
                          [867884, 984655],[322013, -69417], [310503, 522857],
                          [1033096, 604885],[-216386, 477532], [893810, -80353]
                         ];

Essentially, each sub-array represents two months, so in this case it's [Month 1, Month 2], [Month 3, Month 4] and so on. Once I have a figure for each sub array, I will then find the average as a number.

I have been able to calculate the following:

let test1 = groupedMonthTotals[0][1];
let test2 = groupedMonthTotals[1][1];
let difference = test2 - test1;

However, it's not feasible for me to manually run each index and child index as the data that I have spans for over 43 months. I have just provided a snapshot for this question.

How can I loop the following logic for it to spit out the difference? Ideally, I'd like to put these values into an array of their own.

CodePudding user response：

Map through the array:

let groupedMonthTotals=[[867884,984655],[322013,-69417],[310503,522857],[1033096,604885],[-216386,477532],[893810,-80353]];

const result = groupedMonthTotals.map(e => e[1] - e[0])
console.log(result)