Takes in a dataframe and returns a dataframe with
    information on the data-types present in each column.
    Parameters:
    df - DataFrame
        Dataframe to summarize

def dtypes_summary(df):
    """ Takes in a dataframe and returns a dataframe with
    information on the data-types present in each column.
    Parameters:
    df - DataFrame
        Dataframe to summarize
    """
    output_df = pd.DataFrame([])
    row_count = df.shape[0]
    row_indexes = ['rows_numerical','rows_string','rows_date_time','category_count','largest_category','rows_na','rows_total']
    for colname in df:
        data = df[colname] # data is the pandas series associated with this column
        # number of numerical values in the column
        rows_numerical = pd.to_numeric(data,errors = 'coerce').count()
        # number of values that can't be coerced to a numerical
        rows_string = row_count - rows_numerical
        # number of values that can be coerced to a date-time object
        rows_date_time = pd.to_datetime(data,errors = 'coerce',infer_datetime_format = True).count()
        # categories in column
        value_counts = data.value_counts().reset_index()
        # number of different values in the dataframe
        categories = len(value_counts)
        # largest category
        largest_category = value_counts.iloc[0,1]
        # number of null/missing values
        rows_na = data.isnull().sum()
        # build the output list
        output_data = [rows_numerical, rows_string, rows_date_time, categories, 
                       largest_category,rows_na,row_count]
        # add to dataframe
        output_df.loc[:,colname] = pd.Series(output_data)

    # row names
    output_df.index = row_indexes
    return output_df