title: Lodash groupby object and combine array
body: <p>I have calendar data looks like</p>
  
  <pre><code>[ 
    { 
      date: 1488128400000,
        details: [ 
          { time: '01.00 - 02.00', title: 'go sleep' } 
        ] 
    },
    { 
      date: 1488128400000,    
        details: [ 
          { time: '05.30 - 06.30', title: 'wakeup' } 
        ]
    },
    { 
      date: 1488301200000,
        details: [ 
          { time: '09.00 - 10.00', title: 'go to school' } 
      ]   
    } 
  ]
  </code></pre>
  
  <p>I want to group the same date and merge each detail array likes this</p>
  
  <pre><code>[ 
    { 
      date: 1488128400000,
        details: [ 
          { time: '01.00 - 02.00', title: 'go sleep' },
          { time: '05.30 - 06.30', title: 'wakeup' } 
        ] 
    },
    { 
      date: 1488301200000,
        details: [ 
          { time: '09.00 - 10.00', title: 'go to school' } 
      ]   
    } 
  ]
  </code></pre>
  
  <p>Can I solve this problem with <strong>Lodash?</strong></p>
  
  <p>I've just studied Lodash and I don't know about this case and don't know keyword for searching this case.</p>
  
  <p>thank you</p>