title: Monthly sum of level using lodash groupby?
body: <p>I have like to make some conversions using lodash groupby to an array of objects.  Applying to 2 keys clazz_id first and then month resulting in the sum of the level.</p>
  <pre><code>import './App.css'
  import _ from 'lodash'
  import { useEffect } from 'react'
  import moment from 'moment'
  import groupBy from 'lodash/groupBy'
  
  const data1 = [
    {
      id: 1,
      clazz_id: 1,
      answers: [
        { level: 8, created_at: '2022-01-19T09:13:42.149+08:00' },
        { level: 1, created_at: '2022-02-19T09:13:42.149+08:00' },
      ],
    },
    {
      id: 2,
      clazz_id: 2,
      answers: [
        { level: 7, created_at: '2022-01-19T09:13:42.149+08:00' },
        { level: 2, created_at: '2022-03-19T09:13:42.149+08:00' },
      ],
    },
    {
      id: 3,
      clazz_id: 2,
      answers: [
        { level: 3, created_at: '2022-01-19T09:13:42.149+08:00' },
        { level: 8, created_at: '2022-02-19T09:13:42.149+08:00' },
      ],
    },
  ]
  
  const App = () =&gt; {
    const data2 = []
  
    useEffect(() =&gt; {
      data1.map((item) =&gt; {
        item.answers.map((e) =&gt; {
          data2.push({
            clazz_id: item.clazz_id,
            level: e.level,
            month: moment(e.created_at).format('MMM'),
          })
        })
      })
      const a = groupBy(data2, 'clazz_id', 'month')
      console.log(a)
    }, [])
  
    return &lt;div className='App'&gt;test&lt;/div&gt;
  }
  
  export default App
  </code></pre>
  <p>However, the month was not applied correctly.  Any help would be greatly appreciated.</p>
  <p>The result should be:</p>
  <pre><code>[{clazz_id: 1, level: 8, month: 'Jan'},
  {clazz_id: 1, level: 1, month: 'Feb'}]
  
  
  [{clazz_id: 2, level: 10, month: 'Jan'},
  {clazz_id: 2, level: 8, month: 'Feb'},
  {clazz_id: 2, level: 2, month: 'Mar'}]
  </code></pre>