Java Data Analysis

Chapter 2. Data Preprocessing

Before data can be analyzed, it is usually processed into some standardized form. This chapter describes those processes.

Relational database tables

In a relational database, we think of each dataset as a table, with each data point being a row in the table. The dataset's signature defines the columns of the table.

Here is an example of a relational database table. It has four rows and five columns, representing a dataset of four data points with five fields:

Last name	First name	Sex	Age	ID
Adams	John	M	26	704601929
White	null	F	39	440163867
Jones	Paul	M	49	602588410
Adams	null	F	30	120096334

Note

There are two null fields in this table.

Because a database table is really a set of rows, the order of the rows is irrelevant, just as the order of the data points in any dataset is irrelevant. For the same reason, a database table may not contain duplicate rows and a dataset may not contain duplicate data points.

Key fields

A dataset may specify that all values of a designated field be unique. Such a field is called a key field for the dataset. In the preceding example, the ID number field...