Converting Categorical Data to Ordered Types in Python

Hello and welcome! In this lesson, we are going to learn how to convert categorical data into ordered types using the Diamonds dataset from the seaborn library. The goal of this lesson is to enable you to transform categorical data into ordered categorical types effectively. Understanding this process is crucial for improving data analysis and visualization.

Categorical data is data that can be divided into groups or categories. For example, the grades students receive (A, B, C, etc.), types of cars (SUV, Sedan, Truck), and the levels of satisfaction in a survey (Poor, Fair, Good, Very Good, Excellent) are all examples of categorical data.

In the Diamonds dataset, we have categorical columns such as cut, color, and clarity:

• cut describes the quality of the diamond cut (e.g., Fair, Good, Very Good, Premium, Ideal).
• color indicates the color grading of a diamond (e.g., D, E, F, G, H, I, J).
• clarity represents the clarity of the diamond (e.g., I1, SI2, SI1, VS2, VS1, VVS2, VVS1, IF).

Converting categorical data to ordered types is essential for several reasons:

• Sorting: Ordered categorical data can be sorted meaningfully.
• Analysis: Many statistical analyses and visualizations require data to be ordered.
• Representation: Ordered types provide a clear hierarchy or ranking for categorical variables.

For example, in the context of diamond quality:

• Cut: Fair < Good < Very Good < Premium < Ideal
• Color: J < I < H < G < F < E < D
• Clarity: I1 < SI2 < SI1 < VS2 < VS1 < VVS2 < VVS1 < IF

To convert the categorical columns in our dataset to ordered types, follow these steps:

1. Define the category order: First, specify the order of the categories for cut, color, and clarity.

   Python

   cut_categories = ['Fair', 'Good', 'Very Good', 'Premium', 'Ideal']
   color_categories = ['J', 'I', 'H', 'G', 'F', 'E', 'D']
   clarity_categories = ['I1', 'SI2', 'SI1', 'VS2', 'VS1', 'VVS2', 'VVS1', 'IF']

2. Convert to categorical types: Use the pd.Categorical method from Pandas to specify the order for each categorical column.

   Python

   diamonds['cut'] = pd.Categorical(diamonds['cut'], categories=cut_categories, ordered=True)
   diamonds['color'] = pd.Categorical(diamonds['color'], categories=color_categories, ordered=True)
   diamonds['clarity'] = pd.Categorical(diamonds['clarity'], categories=clarity_categories, ordered=True)

3. Verify the conversion: Print the cat.ordered attribute to confirm that the columns have been converted correctly. You can also confirm the order of the categories by accessing categories, as shown in the code below.

   Python

   # Confirm the conversions
   print(diamonds['cut'].cat.ordered)
   print(diamonds['color'].cat.ordered)
   print(diamonds['cut'].cat.ordered)
   
   # Print the order
   print(diamonds['cut'].cat.categories)

The output of the above code will be:

True
True
True
Index(['Fair', 'Good', 'Very Good', 'Premium', 'Ideal'], dtype='object')

This output shows the data types of each column after conversion, indicating that cut, color, and clarity have been successfully converted to ordered categorical types, which will allow for more meaningful sorting and analysis.