title: PHP- Remove keys from invalid json
body: <p>I am new to php and dont know how to deal with invalid json.
  So I want to remove those keys which have invalid string values</p>
  
  <p>Here <code>tag_list</code> and <code>description</code> have invalid string values.</p>
  
  <pre><code>$json='{
      "kind": "track",
      "id": 132453675,
      "created_at": "2014/02/01 02:01:11 +0000",
      "user_id": 895073,
      "duration": 323242,
      "commentable": true,
      "state": "finished",
      "original_content_size": 7745028,
      "last_modified": "2014/02/23 15:48:45 +0000",
      "sharing": "public",
      "tag_list": "hi " how are",
      "permalink": "leaman",
      "streamable": true,
      "embeddable_by": "all",
      "downloadable": false,
      "purchase_url": null,
      "label_id": null,
      "purchase_title": null,
      "genre": "Pop",
      "title": "Leaman",
      "description": "what"" is for",
      "label_name": null,
      "release": null,
      "track_type": null,
      "key_signature": null,
      "isrc": null,
      "video_url": null,
      "bpm": null,
      "release_year": null,
      "release_month": null,
      "release_day": null,
      "original_format": "mp3",
      "license": "all-rights-reserved",
      "uri": "https://api.soundcloud.com/tracks/132453675",
      "user": {
          "id": 895073,
          "kind": "user",
          "permalink": "cloudsareghosts",
          "username": "cloudsareghosts",
          "last_modified": "2014/02/13 22:16:09 +0000",
          "uri": "https://api.soundcloud.com/users/895073",
          "permalink_url": "http://soundcloud.com/cloudsareghosts",
          "avatar_url": "https://i1.sndcdn.com/avatars-000005407842-c7dt3c-large.jpg"
      },
      "permalink_url": "http://soundcloud.com/cloudsareghosts/leaman",
      "artwork_url": "https://i1.sndcdn.com/artworks-000069579796-mhc0bg-large.jpg",
      "waveform_url": "https://w1.sndcdn.com/r4xyDo8zqpfU_m.png",
      "stream_url": "https://api.soundcloud.com/tracks/132453675/stream",
      "playback_count": 253,
      "download_count": 0,
      "favoritings_count": 4,
      "comment_count": 0,
      "attachments_uri": "https://api.soundcloud.com/tracks/132453675/attachments",
      "policy": "ALLOW"
  }';
  </code></pre>
  
  <p>So how can I remove these keys <code>tag_list</code> and <code>description</code> from this json in php.</p>
  
  <p>Thanks</p>