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2.6.1 Retrieving Columns: Indexing by Column Name

            Sometimes, we may be interested in knowing only the names of the products in rather than the complete details of the
            products. The names of the products in the column Product can be retrieved using Product as the column index:

             >>> productNames = groceryDF['Product']
             >>> print(productNames)
            output:
                 0         Bread
                 1          Milk
                 2       Biscuit
                 3    Bourn-Vita
                 4          Soap
                 5         Brush
                 6     Detergent
                 7       Tissues
                 Name: Product, dtype: object
            The above process of selecting a subset of data in a DataFrame is known as indexing. Note that by default, a Pandas
            DataFrame is indexed by columns. Further, note that it is in contrast to series, where indexes correspond to row labels.
            We may also access a column (say, Product) as an attribute of groceryDF, as shown below:
             >>> groceryDF.Product
            output:
                 0         Bread
                 1          Milk
                 2       Biscuit
                 3    Bourn-Vita
                 4          Soap
                 5         Brush
                 6     Detergent
                 7       Tissues
                 Name: Product, dtype: object
            Suppose, we wish to retrieve the product purchased and their prices. For this purpose, we specify the names of
            attributes Product and Price of the DataFrame groceryDF in the form of a list, as shown below:

             >>> groceryDF[['Product', 'Price']]
            output:
                      Product    Price
                 0    Bread         20
                 1    Milk          60
                 2    Biscuit       20
                 3    Bourn-Vita    70
                 4    Soap          40
                 5    Brush         30
                 6    Detergent     80
                 7    Tissues       30
            2.6.2 Indexing by Row Label
            Sometimes, We need to access the details of a particular product, say, the third product, in DataFrame. For this
            purpose, we specify that we are interested in the details of the product at location 2 (row indexes begin with 0), as
            illustrated below:
             >>> groceryDF.loc[2]
            output:
                 Product     Biscuit
                 Category       Food
                 Price            20
                 Quantity          2
                 Name: 2, dtype: object

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