Introduction to Tablesaw

Importing Data in Java

Anthony Markham

VP Quant Developer

Importing Tablesaw

A library for data manipulation
Most common import: import tech.tablesaw.api.*
Additional imports for specific functionality, for example:
- import tech.tablesaw.api.DoubleColumn
- import tech.tablesaw.api.StringColumn
Statistical operations: import tech.tablesaw.aggregate.*

¹ https://jtablesaw.github.io/tablesaw/

Tabular format

Data organized in rows and columns
Columns = variables/features
Rows = observations/instances

An image showing a sample table, with columns and rows labelled.

Tabular format

Can use arrays or collections to store data

// Traditional Java approach (cumbersome)
import java.util.Arrays;
import java.util.List;

List<String> names = Arrays.asList("Anna", "Bob", "Carlos");
List<Integer> ages = Arrays.asList(25, 34, 42);

Creating a table

Options: from scratch, from an external file, or from existing columns

// Creating from scratch
Table employees = Table.create("Employees")
    .addColumns(
        StringColumn.create("Name", "John", "Lisa", "Omar"),
        DoubleColumn.create("Salary", 50000, 60000, 55000)
    );

// From existing columns
StringColumn dept = StringColumn.create("Department", 
    "Sales", "Marketing", "Engineering");
Table departments = Table.create("Departments", dept);

addColumns() and create() methods

Table metadata

Dimensions: table.shape()
Column names: table.columnNames()
Table structure: table.structure()
Preview data: table.first(n), table.last(n)

// Print dimensions
System.out.println(data.shape());  // [rows, columns]

[10, 4]

Table metadata

// Print column names
System.out.println(table.columnNames());

[Day, Temperature, Precipitation]

// Print detailed structure
System.out.println(table.structure());

         Structure of table          
 Index  |   Column Name   |  Column Type  |
     0  |            Day  |       STRING  |
     1  |    Temperature  |       DOUBLE  |
     2  |  Precipitation  |       DOUBLE  |

Table metadata

// Preview first three rows
System.out.println(table.first(3));

                  table                  
    Day     |  Temperature  |  Precipitation  |
    Monday  |         22.5  |              0  |
   Tuesday  |           24  |            2.5  |
 Wednesday  |         23.2  |            5.2  |

Adding columns

Adding columns: table.addColumns(newColumn)

// Add a new column
DoubleColumn bonus = DoubleColumn.create("Bonus", 1000, 1500, 2000);
employees = employees.addColumns(bonus);

Removing and renaming columns

// Remove a column
employees = employees.removeColumns("StartDate");

// Rename a column
employees.column("Salary").setName("AnnualSalary");

// Get the type of column
employees.column("Salary").type();

ColumnType.INTEGER

Modified tables are returned 💡

Summary

Method/Syntax	Description
`Table.create("TableName")`	Creates a new table with the given name
`StringColumn.create("ColumnName", values)`	Creates a string column
`table.shape()`	Returns dimensions as [rows, columns]
`table.columnNames()`	Returns column names in the table
`table.structure()`	Displays table structure information
`table.first(n)`	Returns the first n rows of the table
`table.last(n)`	Returns the last n rows of the table
`table.addColumns(newColumn)`	Adds a new column to the table

¹ https://www.javadoc.io/doc/tech.tablesaw/tablesaw-core

Let's practice!

Importing Data in Java