JAVA將字符串CSV文件轉換爲double []數組

Question

我知道有很多關於將CSV文件轉換爲字符串或整數的問題，但它們並不真正滿足我的需求。

我有一個CSV文件的問題：這是一個文件的示例。

4.98 24 
9.14 21.6 
4.03 34.7 
2.94 33.4 
5.33 36.2 
5.21 28.7 
12.43 22.9 
19.15 27.1 
29.93 16.5 
17.1 18.9 
20.45 15 
13.27 18.9 
15.71 21.7 
8.26 20.4 
10.26 18.2 
8.47 19.9 
6.58 23.1 
14.67 17.5 
11.69 20.2 
11.28 18.2 

目的是將其轉換在類似的東西：

double[] column1= {4.98, 9.14, 4.03, 2.94, 5.33, 5.21, 12.43, 19.15}; //but with all the values, here it's just a sample 
double [] column2 = {24, 21.6, 34.7, 33.4, 36.2, 28.7, 22.9, 27.1}; 

我不想寫的所有數據，我需要做一個循環，但我不知道我是怎麼可以做到。

我設法讀取csv文件並拆分數據但不將結果轉換爲double []數組。這裏是我如何閱讀文件：

String fileName = "dataset.csv"; 
        File file = new File(fileName); 
        String[] values; 
        try{ 
         Scanner inputStream = new Scanner(file); 
         while (inputStream.hasNext()){ 
          String data = inputStream.next(); 
          values = data.split(","); 
         } 
         inputStream.close(); 

        } 
        catch (FileNotFoundException e){ 
         e.printStackTrace(); 
        } 

如果你能幫助我，那會很棒！

Answer 1

下面是Java 7的一個完整的工作示例：

import java.io.File; 
import java.io.IOException; 
import java.util.ArrayList; 
import java.util.Arrays; 
import java.util.List; 
import java.util.Scanner; 

public class Example 
{ 
    public static void main(String args[]) 
    { 
     Scanner inputStream = null; 
     try 
     { 
      String fileName = "dataset.csv"; 
      File file = new File(fileName); 

      // we don't know the amount of data ahead of time so we use lists 
      List<Double> col1 = new ArrayList<>(); 
      List<Double> col2 = new ArrayList<>(); 

      inputStream = new Scanner(file); 
      while (inputStream.hasNext()) 
      { 
       String data = inputStream.next(); 
       String [] arr = data.split(","); 

       col1.add(Double.parseDouble(arr[0])); 
       col2.add(Double.parseDouble(arr[1])); 
      } 

      // Covert the lists to double arrays 
      double[] column1 = new double[col1.size()]; 
      double[] column2 = new double[col2.size()]; 

      for (int i = 0; i < col1.size(); i++) 
      { 
       column1[i] = col1.get(i); 
      } 

      for (int i = 0; i < col2.size(); i++) 
      { 
       column2[i] = col2.get(i); 
      } 

      // print out just for verification 
      System.out.println(Arrays.toString(column1)); 
      System.out.println(Arrays.toString(column2)); 
     } 
     catch (IOException e) 
     { 
      e.printStackTrace(); 
     } 
     finally 
     { 
      if (inputStream != null) 
      { 
       inputStream.close(); 
      } 
     } 
    } 
} 

Answer 2

您可以將文件中的行分流並將它們拆分爲String[]，就像您一樣。然後，您可以流每個這樣的陣列，並且每個項目轉換爲double，然後收集他們回到陣列：

double[][] data = 
    Files.lines(Paths.get(fileName)) 
     .map(s -> s.split(",")) 
     .map(s -> Arrays.stream(s).mapToDouble(Double::parseDouble).toArray()) 
     .toArray(double[][]::new);