请问这里为什么没有Aggregation?

问题如下：

After cleansing the data, Steele then preprocesses the dataset. She creates two new variables: an “Age” variable based on the firm’s IPO date and an “Interest Coverage Ratio” variable equal to EBIT divided by interest expense. She also deletes the “IPO Date” variable from the dataset.

During the preprocessing of the data in Exhibit 1, what type of data transformation did Steele perform during the data preprocessing step?

选项：

Extraction

Conversion

Aggregation

解释：

A is correct. During the data preprocessing step, Steele created a new “Age” variable based on the firm’s IPO date and then deleted the “IPO Date” variable from the dataset. She also created a new “Interest Coverage Ratio” variable equal to EBIT divided by interest expense. Extraction refers to a data transformation where a new variable is extracted from a current variable for ease of analyzing and using for training an ML model, such as creating an age variable from a date variable or a ratio variable. Steele also performed a selection transformation by deleting the IPO Date variable, which refers to deleting the data columns that are not needed for the project.