 operation has been performed
    &#34;&#34;&#34;
    df[classification_col].fillna(0, inplace=True)
    return df

#Merge lithologies to main df based on classifications
def merge_lithologies(well_data_df, targinterps_df, interp_col=&#39;INTERPRETATION&#39;, target_col=&#39;TARGET&#39;, target_class=&#39;bool&#39;):
    &#34;&#34;&#34;Function to merge lithologies and target booleans based on classifications
    
    Parameters
    ----------
    well_data_df : pandas.DataFrame
        Dataframe containing