Очистка и стандартизация столбцов

Очистка данных на Java

Dennis Lee

Software Engineer

Набор данных о продажах книг

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

Изучение типов данных

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());
}

Изучение типов данных: вывод

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

Преобразование числовых форматов

// 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();

Умножение столбцов

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());

Умножение столбцов: вывод

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           |

Регулярное выражение для скобок

Шаблон \\(.*\\) соответствует круглым скобкам
Примеры совпадений: "(Organic)", "(2 pack)", "(Large)"
Результат: "Apple (Organic)" становится "Apple"

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

Обработка специальных символов

// 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

Комбинирование строковых операций

// 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

Подводим итоги

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

Давайте потренируемся!

Очистка данных на Java