Data structures in Tablesaw

Importing Data in Java

Anthony Markham

VP Quant Developer

Core data structures

Table: Primary container (like a DataFrame)

Table employees = Table.create("Employees");

Column: Holds values of a consistent type

StringColumn nameCol = StringColumn.create("Name");

Row: Represents individual records

Row firstRow = employees.row(0);

Table methods

String tableName = employees.name();

employees

// Row and column counts
int rowCount = employees.rowCount();
int columnCount = employees.columnCount();

1000
5

Column types

Strong typing = each column has fixed data type
- Improves performance and makes code easier to debug
Examples:
- StringColumn - Text data
- IntColumn, DoubleColumn - Numeric values
- BooleanColumn - True/False values
- Time series data:
  - DateColumn - calendar dates (2024-03-05)
  - DateTimeColumn - datetime (2024-03-05T14:32)

Column type operations

Each type provides specialized operations

// Using .mean() on DoubleColumn
DoubleColumn salary = employees.column("Salary");
double averageSalary = salary.mean();

Accessing data

// Get a specific column
StringColumn names = employees.stringColumn("Name");


// Get a general column
names = employees.column("Name");


// Get a value from a column
String firstPerson = names.get(0);


// Get an entire row
Row firstRow = employees.row(0);


// Get a value from a row
double salary = firstRow.getDouble("Salary");

Selections

Set of row indices that match a condition
Examples:
- .isGreaterThan(), .isLessThan()
- .isEqualTo()
- .isAfter()

// Create a selection of rows
Selection highEarners = employees.doubleColumn("Salary")
    .isGreaterThan(70000);

Filtering on a Selection

// Create a selection of rows
Selection highEarners = employees.doubleColumn("Salary")
    .isGreaterThan(70000);


// Apply selection to get a filtered table
Table highPaidEmployees = employees.where(highEarners);

.where() returns a new table

Boolean operations

Combine selections with .and() and .or()

Selection recentHires = employees.dateColumn("HireDate")
    .isAfter(LocalDate.of(2020, 1, 1));

Selection highPaidRecent = highEarners.and(recentHires);

Let's practice!

Importing Data in Java