Group by key + merge array values
<p>I'm trying to merge the array values of multiple arrays with same keys (sort of group by + merge).  Is there any native way in Go to transform this input:  </p>

<pre><code>input = [
    [
        { a: 1, b: [1,2]},
        { a: 2, b: [1,2]},
        { a: 3, b: [1,2]}
    ],
    [
        { a: 1, b: [3,4]},
        { a: 2, b: [3,4]},
        { a: 3, b: [3,4]},
        { a: 4, b: [3,4]}
    ],
    [
        { a:1, b: [5,6]},
        { a:2, b: [5,6]},
        { a:3, b: [5,6]},
        { a:4, b: [5,6]},
        { a:5, b: [5,6]}
    ]
 ]
</code></pre>

<p>into:</p>

<pre><code>output = [
    { a: 1, b: [1,2,3,4,5,6]},
    { a: 2, b: [1,2,3,4,5,6]},
    { a: 3, b: [1,2,3,4,5,6]},
    { a: 4, b: [3,4, 5,6]},
    { a: 5, b: [5,6]},
]
</code></pre>