Column cleaning and standardization

Cleaning Data in Java

Dennis Lee

Software Engineer

Book sales dataset

Books	Authors	Language	First_Published	Sales_in_Millions	Average_Price
A Tale of Two Cities	Charles Dickens	English	1859	200.0	12.99
The Little Prince (Le Petit Prince)	Antoine de Saint-Exupéry	French	1943	200.0	15.50
Harry Potter and the Philosopher's Stone	J. K. Rowling	English	1997	120.0	19.99
And Then There Were None	Agatha Christie	English	1939	100.0	14.95

Examining data types

import tech.tablesaw.api.Table;
import tech.tablesaw.api.StringColumn;
import tech.tablesaw.api.DoubleColumn;

Table books = Table.read().csv("bestsellers.csv");

for (String colName : books.columnNames()) {

    // Print column name and its type
    System.out.println(colName + ": " + books.column(colName).type());
}

Examining data types: outputs

Books: STRING
Authors: STRING
Language: STRING
First_Published: INTEGER
Sales_in_Millions: INTEGER
Average_Price: DOUBLE

Converting numeric formats

// Convert IntColumn to DoubleColumn since Tablesaw inferred it as INTEGER
DoubleColumn sales = books.intColumn("Sales_in_Millions")
      .asDoubleColumn();

System.out.println("Data type of sales column after conversion: " + sales.type());

Data type of sales column after conversion: DOUBLE

// It's possible to convert a DoubleColumn to an IntColumn
IntColumn salesAsInt = sales.asIntColumn();

Multiplying columns

DoubleColumn averagePrice = books.doubleColumn("Average_Price");

// Calculate total revenue by multiplying two columns
DoubleColumn totalRevenue = sales.multiply(averagePrice)

        .setName("Total_Revenue_Millions");

books.addColumns(totalRevenue);

System.out.println("\nMultiplying two columns: Sales × Price = Revenue");
System.out.println(books.selectColumns("Books", "Sales_in_Millions", 
                                       "Average_Price", "Total_Revenue_Millions")
        .first(4).print());

Multiplying columns: outputs

Multiplying two columns: Sales * Price = Revenue

| Books                               | Sales_in_  | Average_  | Total_Revenue_ |
|                                     | Millions   | Price     | Millions       |
|-------------------------------------|------------|-----------|----------------|
| A Tale of Two Cities                | 200        | 12.99     | 2598           |
| The Little Prince (Le Petit Prince) | 200        | 15.50     | 3100           |
| Harry Potter and                    | 120        | 19.99     | 2398.80        |
|   the Philosopher's Stone           |            |           |                |
| And Then There Were None            | 100        | 14.95     | 1495           |

Regex to match parentheses

The pattern \\(.*\\) matches parentheses
Example matches: "(Organic)", "(2 pack)", "(Large)"
Result: "Apple (Organic)" becomes "Apple"

\\(     // Match opening parenthesis (escaped with \)
.*      // Match any character (.) zero or more times (*)
\\)     // Match closing parenthesis (escaped with \)

Handling special characters

// Remove parenthetical translations from titles
StringColumn titlesNoParentheses = titles
        // For each title in titles, remove parentheses and surrounding spaces
        .map(t -> t.replaceAll("\\(.*\\)", "").trim())
        // Set the new column name
        .setName("Titles without parentheses");

System.out.println("Original: " + titles.get(1)); // Get the first column item
System.out.println("Cleaned: " + titlesNoParentheses.get(1));

Original: The Little Prince (Le Petit Prince)
Cleaned: The Little Prince

Combining string operations

// Combine removing parentheses and converting to lowercase
StringColumn titlesCombinedCleaning =
        titles.map(t -> t.replaceAll("\\(.*\\)", "") // Remove parentheses

                         .trim() // Remove surrounding space

                         .toLowerCase()) // Convert to lowercase
              .setName("Clean_Titles_Combined"); // Set column name

System.out.println("Original title: " + titles.get(1));
System.out.println("Title after cleaning: " + titlesCombinedCleaning.get(1));

Original title: The Little Prince (Le Petit Prince)
Title after cleaning: the little prince

Putting it all together

books.column(colName).type(); // Get column type
books.intColumn("Sales_in_Millions").asDoubleColumn(); // Convert type

DoubleColumn totalRevenue = sales.multiply(averagePrice) // Multiply columns
    .setName("Total_Revenue_Millions"); // Name new column

titles.map(String::toLowerCase) // Convert to lowercase
    .setName("Lowercase_Titles"); // Name new column

titles.map(t -> t.replaceAll("\\(.*\\)", "").trim()) // Remove parentheses
    .setName("Titles without parentheses"); // Name new column

Let's practice!

Cleaning Data in Java