Calculate increase/decrease between object key pair values
<p>I have an object, populated with objects like this: </p>

<pre><code>tblValArr = {
  2015: { 
    jan: 32.75, 
    feb: 58.65, 
    mar: 13.28, 
    apr: 35.78, 
    may: 98.45, 
    jun: 45.69, 
    jul: 32.68, 
    aug: 75.45,
    sep: 39.87,
    oct: 95.48,
    nov: 26.78,
    dec: 12.17
  },
  2016: { 
    jan: 48.12, 
    feb: 13.56, 
    mar: 57.54, 
    apr: 14.01, 
    may: 45.84, 
    jun: 84.12, 
    jul: 78.68, 
    aug: 18.10
    ...
    ...
    ...
    ...
  },
};
</code></pre>

<p>Now i want to calculate the increase/decrease in percent between each key value pair (month) between 2016-2015. </p>

<p>Note: The array can have more than just 2 years. But I only want to do the calculations between the two latest years added to the array.</p>

<p>So, the result im looking for would be a new object that looks something like: </p>

<pre><code>newArrOfDiffs = { 
    jan: 46.93%, 
    feb: -76.87%, 
    mar: ..., 
    apr: ..., 
    may: ..., 
    jun: ..., 
    jul: ..., 
    aug: ...,
    sep: ...,
    oct: ...,
    nov: ...,
    dec: ...
  },
</code></pre>

<p>How do i achieve this? </p>