def impute_with_median (df):
    """Iterate through columns of Pandas DataFrame.
    Where NaNs exist replace with median"""
    
    # Get list of DataFrame column names
    cols = list(df)
    # Loop through columns
    for column in cols:
        # Transfer column to independent series
        col_data = df[column]
        # Look to see if there is any missing numerical data
        missing_data = sum(col_data.isna())
        if missing_data > 0:
            # Get median and replace missing numerical data with median
            col_median = col_data.median()
            col_data.fillna(col_median, inplace=True)
            df[column] = col_data
    return df


def plot_roc_curve(fpr, tpr, label=None):
    """Plot the ROC curve from False Positive Rate 
    and True Positive Rate"""
    
    plt.plot(fpr, tpr, linewidth=2, label=label)
    plt.plot([0, 1], [0, 1], 'k--') 
    plt.axis([0, 1, 0, 1])                       
    plt.xlabel('False Positive Rate', fontsize=16)
    plt.ylabel('True Positive Rate', fontsize=16)
    plt.grid(True)