def sorted_word_count(df): 
    """Returns a Pandas DataFrame of posts sorted by mean word count per day.

    Args: 
        df: A Pandas DataFrame
    
    Returns:
        Pandas DataFrame
    """

    df = df.copy()
    df['created'] = df['created'].dt.date
    
    return (df[['created', 'word_count']]
     .groupby('created')
     .agg('mean')
     .reset_index()
     .sort_values(by='created'))