title: jq count the number of items in json by a specific key
body: <p>The following is the first two items in my json file</p>
  
  <pre><code>{
  "ReferringUrl": "N",
  "OpenAccess": "0",
  "Properties": {
      "ItmId": "1694738780"
     }
  }
  {
  "ReferringUrl": "L",
  "OpenAccess": "1",
  "Properties": {
      "ItmId": "1347809133"
    }
  }
  </code></pre>
  
  <p>I want to count the number of items by each ItmId appeared in the json. For example, items that with "ItmId" 1694738780 appears 10 times and items with "ItmId" 1347809133 appears 14 times in my json file. Then return a json like this</p>
  
  <pre><code>{"ItemId": "1694738780",
   "Count":  10
  }
  {"ItemId": "1347809133",
   "Count":  14
  }
  </code></pre>
  
  <p>I am using bash. And prefer do this totally by jq. But it's ok to use other method.</p>
  
  <p>Thank you!!!</p>