title: Get all unique key from nested object
body: <p>I have this object:</p>
  
  <pre><code>{
    "apple": {
      "0": {
        "2018-04-25 19:51:38": {
          "x": "38.0",
          "y": "23.0"
        },
        "2018-04-25 19:51:39": {
          "x": "NaN",
          "y": "NaN"
        },
        "2018-04-25 19:51:40": {
          "x": "NaN",
          "y": "NaN"
        }
      },
      "5": {
        "2018-04-25 19:51:38": {
          "x": "50.0",
          "y": "35.0"
        },
        "2018-04-25 19:51:43": {
          "x": "21.0",
          "y": "3.0"
        }
      },
      "6": {
        "2018-04-25 19:51:34": {
          "x": "30.0",
          "y": "15.0"
        },
        "2018-04-25 19:51:39": {
          "x": "NaN",
          "y": "NaN"
        },
        "2018-04-25 19:52:40": {
          "x": "22.0",
          "y": "20.0"
        },
        "2018-04-25 19:52:42": {
          "x": "33.0",
          "y": "45.0"
        }
      }
    },
    "team": {
      "2": {
        "2018-04-25 19:51:35": {
          "x": "32.0",
          "y": "25.0"
        },
        "2018-04-25 19:51:36": {
          "x": "33.0",
          "y": "40.0"
        },
        "2018-04-25 19:51:37": {
          "x": "12.0",
          "y": "24.0"
        },
        "2018-04-25 19:51:38": {
          "x": "33.0",
          "y": "45.0"
        }
      },
      "3": {
        "2018-04-25 19:51:35": {
          "x": "2.0",
          "y": "3.0"
        },
        "2018-04-25 19:51:36": {
          "x": "4.0",
          "y": "5.0"
        },
        "2018-04-25 19:51:37": {
          "x": "12.0",
          "y": "15.0"
        },
        "2018-04-25 19:51:38": {
          "x": "33.0",
          "y": "45.0"
        }
      },
      "4": {
        "2018-04-25 19:51:35": {
          "x": "20.0",
          "y": "30.0"
        },
        "2018-04-25 19:51:36": {
          "x": "41.0",
          "y": "35.0"
        },
        "2018-04-25 19:51:37": {
          "x": "32.0",
          "y": "65.0"
        },
        "2018-04-25 19:51:38": {
          "x": "43.0",
          "y": "49.0"
        }
      },
      "5": {
        "2018-04-25 19:51:35": {
          "x": "21.0",
          "y": "33.0"
        },
        "2018-04-25 19:51:36": {
          "x": "31.0",
          "y": "12.0"
        },
        "2018-04-25 19:51:37": {
          "x": "34.0",
          "y": "54.0"
        },
        "2018-04-25 19:51:38": {
          "x": "93.0",
          "y": "22.0"
        }
      }
    }
  }
  </code></pre>
  
  <p>What I want are two array of unique timestamps: one for <code>apple</code> and one for <code>team</code>.
  So:</p>
  
  <pre><code>const appleTimestamps = ["2018-04-25 19:51:34", "2018-04-25 19:51:37", "2018-04-25 19:51:38", "2018-04-25 19:51:39", "2018-04-25 19:51:40", "2018-04-25 19:51:43", "2018-04-25 19:52:40", "2018-04-25 19:52:42"]
  const teamTimestamps = ["2018-04-25 19:51:35", "2018-04-25 19:51:36", "2018-04-25 19:51:37", "2018-04-25 19:51:38"]
  </code></pre>
  
  <p>As you can see, keys inside Apple and team are not sequential.
  How can I do that? The only way i thought is use <code>find</code> but I'm sure I'm wrong.</p>
  
  <p>(I can use also <em>Lodash</em>)</p>