Prompt Title: Selecting multiple columns with conditions in Tablesaw.

Tablesaw is a Java library for data manipulation and analysis. It allows you to perform various operations on tables, such as filtering, sorting, and aggregation. To select multiple columns from two tables with multiple WHERE cases, you'll need to follow these steps:

1. Load the tables into Tablesaw.
2. Perform the necessary filtering using the .where() method with multiple conditions.
3. Select the desired columns using the .select() method.
4. Join the two tables on a common key if necessary.
5. Extract the final result.

Here's an example demonstrating how to achieve this:

javaCopy code
import tech.tablesaw.api.*;
import tech.tablesaw.columns.Column;
import static tech.tablesaw.aggregate.AggregateFunctions.*;
import static tech.tablesaw.api.QuerySupport.*;

public class TablesawExample {
    public static void main(String[] args) {
        // Load the tables
        Table table1 = Table.read().csv("table1.csv");
        Table table2 = Table.read().csv("table2.csv");

        // Apply multiple WHERE cases to both tables
        Table filteredTable1 = table1.where(
                and(
                        table1.stringColumn("columnA").isEqualTo("value1"),
                        table1.numberColumn("columnB").isGreaterThanOrEqualTo(100)
                )
        );

        Table filteredTable2 = table2.where(
                and(
                        table2.stringColumn("columnC").isEqualTo("value2"),
                        table2.numberColumn("columnD").isLessThanOrEqualTo(200)
                )
        );

        // Select the desired columns from both tables
        Table selectedColumnsTable1 = filteredTable1.select("columnA", "columnB");
        Table selectedColumnsTable2 = filteredTable2.select("columnC", "columnD", "joinKey");

        // Join the two tables on a common key if necessary
        Table joinedTable = selectedColumnsTable1.joinOn("joinKey").inner(selectedColumnsTable2);

        // Print the final result
        System.out.println(joinedTable.printAll());
    }
}

In this example, we first load two tables from CSV files, then apply multiple WHERE conditions to both tables using the where() method. We use the and() method to combine multiple conditions. After filtering, we select the desired columns from both tables using the select() method. Finally, if necessary, we join the two tables on a common key and print the final result.

Apologies for the confusion. You're right, the select() method is deprecated in the latest Tablesaw versions. Instead, you should use the retainColumns() method to select specific columns. Here's the updated example:

javaCopy code
import tech.tablesaw.api.*;
import tech.tablesaw.columns.Column;
import static tech.tablesaw.aggregate.AggregateFunctions.*;
import static tech.tablesaw.api.QuerySupport.*;

public class TablesawExample {
    public static void main(String[] args) {
        // Load the tables
        Table table1 = Table.read().csv("table1.csv");
        Table table2 = Table.read().csv("table2.csv");

        // Apply multiple WHERE cases to both tables
        Table filteredTable1 = table1.where(
                and(
                        table1.stringColumn("columnA").isEqualTo("value1"),
                        table1.numberColumn("columnB").isGreaterThanOrEqualTo(100)
                )
        );

        Table filteredTable2 = table2.where(
                and(
                        table2.stringColumn("columnC").isEqualTo("value2"),
                        table2.numberColumn("columnD").isLessThanOrEqualTo(200)
                )
        );

        // Select the desired columns from both tables
        Table selectedColumnsTable1 = filteredTable1.retainColumns("columnA", "columnB", "joinKey");
        Table selectedColumnsTable2 = filteredTable2.retainColumns("columnC", "columnD", "joinKey");

        // Join the two tables on a common key if necessary
        Table joinedTable = selectedColumnsTable1.joinOn("joinKey").inner(selectedColumnsTable2);

        // Print the final result
        System.out.println(joinedTable.printAll());
    }
}

In this updated example, we replace the deprecated select() method with the retainColumns() method to select the desired columns from the filtered tables. The rest of the example remains the same.