進階資料操作技巧

Java 中的資料匯入

Anthony Markham

VP Quant Developer

刪除與新增欄

用 .drop() 刪除不需要的欄
用 .addColumns() 新增預先計算或類別欄
- 列數必須相同 ❗

// Remove specific columns
Table cleaned = dataTable.drop("TempID", "Notes");


// Add two new columns
StringColumn statusCol = StringColumn.create("Status", "Active", "Inactive", "Active");
IntColumn priorityCol = IntColumn.create("Priority", 1, 2, 3);

Table enhanced = dataTable.addColumns(statusCol, priorityCol);

用 .dropWhere() 篩列

移除符合條件的列
使用 Selection 作為篩選條件

// Create a selection condition
Selection outliers = dataTable.doubleColumn("Value")
    .isLessThan(lowerBound)
    .or(dataTable.doubleColumn("Value")
        .isGreaterThan(upperBound));


// Remove rows matching the condition
Table cleanedData = dataTable.dropWhere(outliers);

列數計算

.rowCount()：計算表格列數

// Compare row counts
System.out.println("Original rows: " + dataTable.rowCount());
System.out.println("After dropping outliers: " + 
    cleanedData.rowCount());

Original rows: 100
After dropping outliers: 95

布林篩選

支援 and、or、not 方法

// Complex boolean filtering
Selection techHighPaid = dataTable.stringColumn("Department")
    .isEqualTo("Technology")
    .and(dataTable.doubleColumn("Salary")
        .isGreaterThan(100000));


// Inverse selection (NOT)
Selection nonTechOrLowPaid = techHighPaid.not();

用 .map() 做轉換

套用函式轉換欄位值
支援 lambda，程式碼更易讀

// Transform an entire column with a predefined function
StringColumn upperNames = dataTable.stringColumn("Name").map(s -> s.toUpperCase());

// Transform values in a column
DoubleColumn prices = dataTable.doubleColumn("Price");
DoubleColumn discounted = prices.map(price -> price * 0.9);


// Set a name and add a column
discounted.setName("DiscountedPrice");
Table withDiscounts = dataTable.addColumns(discounted);

重點整理

.drop()：從表格移除欄
.dropWhere()：移除符合條件的列
.addColumns()：為表格新增欄
.map()：轉換欄位值

// Core advanced manipulation methods
dataTable.drop("TemporaryID");              
dataTable.dropWhere(selection);             
dataTable.addColumns(newColumn);            
doubleCol.map(value -> value * 2);

一起來練習吧！

Java 中的資料匯入