title: When creating a seaborn heatmap 'could not convert string to float' ValueError
body: <p>Hi everyone I have the following dataframe and I want to create heatmap from it with the following code.</p>
  <p><a href="https://i.stack.imgur.com/FWUhU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FWUhU.png" alt="My DataFrame" /></a></p>
  <pre><code>plt.figure(figsize=(10,10))
  g = sns.heatmap(
      top_5_stations_hourly_total_traffic_by_time, 
      square=True,
      cbar_kws={'fraction' : 0.01},
      cmap='OrRd',
      linewidth=1
  )
  
  g.set_xticklabels(top_5_stations_hourly_total_traffic_by_time.STATION, rotation=45, horizontalalignment='right')
  g.set_yticklabels(top_5_stations_hourly_total_traffic_by_time.TIME, rotation=45, horizontalalignment='right')
  </code></pre>
  <p>But it gives the following error :</p>
  <blockquote>
  <blockquote>
  <blockquote>
  <p>ValueError: could not convert string to float: '125 ST'</p>
  </blockquote>
  </blockquote>
  </blockquote>