如何将 csv 文件中的数字保存到 java 数组列表中

Question

你好，这是我第一次发帖，如果我在提问过程中做错了什么，请告诉我。

我的目的：将双变量保存在 csv 文件中，并将它们保存在 java 文件中的数组列表中。

我目前有当前代码，我是java初学者，所以请不要喷ToT

import java.io.*;
import java.util.*;
import java.lang.*;

public class CsvProcessor {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);

        // ask for file path at command prompt, save the path input in path
        System.out.print("path of file: ");
        String path = keyboard.next();

        try {
            // set up file, reader, and arraylist for processing csv file
            java.io.File csv = new java.io.File(path);
            BufferedReader bufferedReader = new BufferedReader(new FileReader(csv));
            ArrayList<String> csvEntry = new ArrayList<String>();

            // set parameters for StringTokenizer
            String line = "";
            String delimiter = ",";

            //read using bufferedReader and save using csvEntry ArrayList
            while ((line = bufferedReader.readLine()) != null) {    
                StringTokenizer stringTokenizer = new StringTokenizer(line, delimiter);
                while (stringTokenizer.hasMoreTokens()) {
                    csvEntry.add(stringTokenizer.nextToken());
                }
            }

            csvEntry.toArray();
            double[] csvDouble = new double[csvEntry.getLength()];
            for (int i = 0; i < csvEntry.getLength(); i++) {
                csvDouble[i] = Double.parseDouble(csvEntry[i]);
            }

            int x = csvDouble.getLength();
            double sum = 0;

            for (int y = 0; y < x; y++) {
                sum = sum + csvDouble[y];
            }

            double mean = sum / x;
            System.out.println("mean is: " + mean);
            bufferedReader.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

我尝试了一些方法，比如转换 csv 文件中的字符串并将它们保存到 arraylist 中，然后将 arraylist 转换为数组，然后再将其转换为 double 数组。 我得到的错误是：

C:\Users\user\Codes\ktrt>java CsvProcessor
path of file: C:\Users\user\Codes\ktrt\montyreal.csv
Exception in thread "main" java.lang.NumberFormatException: For input string: "5
48.53"
        at java.lang.NumberFormatException.forInputString(Unknown Source)
        at java.lang.Integer.parseInt(Unknown Source)
        at java.lang.Integer.<init>(Unknown Source)
        at CsvProcessor.main(csvprocessor.java:27)

非常感谢您的帮助。

Answer 1

首先，你有一个错误的错误日志。您的代码没有 Integer.parseInt() 方法。假设您正确地将 CSV 解析为 csvEntry 变量，您可以这样做：

List<Double> csvDouble = new ArrayList<Double>();
double mean, total = 0;

for (String raw : csvEntry) {
  double entry = Double.valueOf(raw);
  total += entry;
  csvDouble.add(entry);
}

mean = total / csvDouble.size();
// at this point you have your ArrayList and mean value;
System.out.println("mean is " + mean);

希望这会有所帮助:)