a function to create a null matrix in python
def plot_null_matrix(df, figsize=(18,15)):
# initiate the figure
plt.figure(figsize=figsize)
# create a boolean dataframe based on whether values are null
df_null = df.isnull()
# create a heatmap of the boolean dataframe
sns.heatmap(~df_null, cbar=False, yticklabels=False)
plt.show()