title: TypeError: ufunc 'isnan' not supported for the input types, - seaborn Heatmap
body: <p>I am getting the error when i try to plot a seaborn heatmap</p>
  
  <p>TypeError: ufunc 'isnan' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''</p>
  
  <p>my code is as follows </p>
  
  <pre><code>import pandas as pd
  import seaborn as sns
  import matplotlib.pyplot as plt
  
  df = pd.read_table(r"C:\Results.CST", sep='\s+',header=11, engine = 'python')
  df2 = cridim[['Bottom','Location_X','Location_Y',]]  # Bottom , location X and Location  Y are my column labels
  df3 = df2.pivot('Location_X','Location_Y','Bottom') # create pivot table for results
  
  plt.figure(figsize=(15,15)) 
  pivot_table = df3
  plt.xlabel('X',size = 10) 
  plt.ylabel('Y',size = 10) 
  plt.title('btm CD',size = 10) 
  sns.heatmap(pivot_table, annot=False, fmt=".1f", linewidths = 0.5, square = True, cmap = 'RdYlBu', vmin=2900, vmax = 3500) 
  plt.show()
  </code></pre>
  
  <p>In my data consist of 77 rows and 77 columns, of which only 651 have data, the others empty coordinates are indicated as None in the dataframe</p>
  
  <p>Is there a limitation of how many data can seaborn heatmap can plot?</p>
  
  <p>I am not sure why am i getting the above  error, I have written it to a csv file and it turns out alright.</p>
  
  <p>in addition, I have try to replace the values to '0' and empty string but it still return the Typeerror </p>