I have never used multiIndex pandas dataframes, and the Python API for CalcBench, a financial program I use, returned one when I typed the following code:

```
dataItems = ["ROE", "StockholdersEquity", "SharesOutstandingEndOfPeriod", "EndOfPeriodStockPrice"]             
data = cb.normalized_data(tickers, dataItems, start_year=2021, end_year=2021, period_type='annual')

```

If I try to explore my dataframe by typing `data.info()`, I get:

```
<class 'pandas.core.frame.DataFrame'>
PeriodIndex: 1 entries, 2021 to 2021
Freq: A-DEC
Columns: 1800 entries, ('EndOfPeriodStockPrice', 'A') to ('StockholdersEquity', 'ZTS')
dtypes: float64(1800)

```

Typing `data.columns()` gives me:

```
MultiIndex([('EndOfPeriodStockPrice',    'A'),
            ('EndOfPeriodStockPrice',  'AAL'),
            ('EndOfPeriodStockPrice',  'AAP'),
            ('EndOfPeriodStockPrice', 'AAPL'),
            ('EndOfPeriodStockPrice', 'ABBV'),
            ('EndOfPeriodStockPrice',  'ABC'),
            ('EndOfPeriodStockPrice',  'ABT'),
            ('EndOfPeriodStockPrice',  'ACN'),
            ('EndOfPeriodStockPrice', 'ADBE'),
            ('EndOfPeriodStockPrice',  'ADI'),
            ...
            (   'StockholdersEquity', 'WYNN'),
            (   'StockholdersEquity',  'XEL'),
            (   'StockholdersEquity',  'XOM'),
            (   'StockholdersEquity', 'XRAY'),
            (   'StockholdersEquity',  'XYL'),
            (   'StockholdersEquity',  'YUM'),
            (   'StockholdersEquity',  'ZBH'),
            (   'StockholdersEquity', 'ZBRA'),
            (   'StockholdersEquity', 'ZION'),
            (   'StockholdersEquity',  'ZTS')],
           names=['metric', 'ticker'], length=1800)

```

I would like to create a new metric `MarketCapAtEndOfPeriod` in this dataframe for each firm in the year 2021 by multiplying the corresponding entries for `EndofPeriodStockPrice` and `SharesOutstandingEndOfPeriod`.

My efforts to do so have gone nowhere, and searching StackOverflow has not helped me solve my problem. Loosely speaking, I'm looking to write something like:

```
data["MarketCapAtEndOfPeriod"] = data["EndofPeriodStockPrice"] * data["SharesOutstandingEndOfPeriod"]

```