title: How to fix "ImportError: Pandas >= 0.19.2 must be installed; however, it was not found"?
body: <p>I use Spark 2.3.1 and want to use <code>toPandas()</code> (to use <code>unique()</code>).</p>
  
  <p>When I execute the following code in <code>pyspark</code>:</p>
  
  <pre><code>df.toPandas()['column_01'].unique()
  </code></pre>
  
  <p>I'm facing the following exception:</p>
  
  <pre><code>&gt;&gt;&gt; df.toPandas()
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/Users/xxx/spark/python/pyspark/sql/dataframe.py", line 2075, in toPandas
      require_minimum_pandas_version()
    File "/Users/xxx/spark/python/pyspark/sql/utils.py", line 129, in require_minimum_pandas_version
      "it was not found." % minimum_pandas_version)
  ImportError: Pandas &gt;= 0.19.2 must be installed; however, it was not found.
  </code></pre>
  
  <p>How to fix it?</p>