如何按升序对文件名进行排序? [英] How to sort file names in ascending order?

问题描述

我在一个文件夹中有一组文件，除了一个之外，所有文件都以相似的名称开头.下面是一个例子:

I have a set of files in a folder, and all of them starting with a similar name, except one. Here is an example:

Coordinate.txt
Spectrum_1.txt
Spectrum_2.txt
Spectrum_3.txt
.
.
.
Spectrum_11235

我可以列出指定文件夹中的所有文件，但列表没有按照光谱编号的升序排列.示例:我在执行程序时得到如下结果:

I am able to list all the files from the specified folder, but the list is not in an ascending order of the spectrum number. Example: I get the following result when the program is executed:

Spectrum_999.txt
Spectrum_9990.txt
Spectrum_9991.txt
Spectrum_9992.txt
Spectrum_9993.txt
Spectrum_9994.txt
Spectrum_9995.txt
Spectrum_9996.txt
Spectrum_9997.txt
Spectrum_9998.txt
Spectrum_9999.txt

但是这个顺序不对.在 Spectrum_999.txt 之后应该有 Spectrum_1000.txt 文件.任何人都可以帮忙吗?代码如下:

But this order is not correct. There should be Spectrum_1000.txt file after Spectrum_999.txt. Can anyone help? Here is the code:

import java.io.*;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

    public class FileInput {

        public void userInput()
        {
            Scanner scanner = new Scanner( System.in );
            System.out.println("Enter the file path: ");
            String dirPath = scanner.nextLine(); // Takes the directory path as the user input

            File folder = new File(dirPath);
            if(folder.isDirectory())
            {
                File[] fileList = folder.listFiles();

                Arrays.sort(fileList);

                System.out.println("\nTotal number of items present in the directory: " + fileList.length );


                // Lists only files since we have applied file filter
                for(File file:fileList)
                {
                    System.out.println(file.getName());
                }

                // Creating a filter to return only files.
                FileFilter fileFilter = new FileFilter()
                {
                    @Override
                    public boolean accept(File file) {
                        return !file.isDirectory();
                    }
                };

                fileList = folder.listFiles(fileFilter);

                // Sort files by name
                Arrays.sort(fileList, new Comparator()
                {
                    @Override
                    public int compare(Object f1, Object f2) {
                        return ((File) f1).getName().compareTo(((File) f2).getName());
                    }
                });

                //Prints the files in file name ascending order
                for(File file:fileList)
                {
                    System.out.println(file.getName());
                }

            }   
        }
    }

推荐答案

你要的是数字排序.您需要实现一个 Comparator 并将其传递给Arrays#sort 方法.在比较方法中，您需要从每个文件名中提取数字，然后比较数字.

What you are asking for is numerical sort. You need implement a Comparator and pass it to the Arrays#sort method. In the compare method you need to extract the number from each filename an then compare the numbers.

你现在得到输出的原因是排序发生字母数字

The reason why you get the output you are getting now is that sorting happens alphanumerically

这是一个非常基本的方法.此代码使用简单的 String 操作来提取数字.如果您知道文件名的格式，则此方法有效，在您的情况下为 Spectrum_.txt.进行提取的更好方法是使用正则表达式.

Here a is a very basic way of doing it. This code uses simple String-operation to extract the numbers. This works if you know the format of the filename, in your case Spectrum_<number>.txt. A better way of doing the extraction is to use regular expression.

public class FileNameNumericSort {

    private final static File[] files = {
        new File("Spectrum_1.txt"),
        new File("Spectrum_14.txt"),
        new File("Spectrum_2.txt"),
        new File("Spectrum_7.txt"),     
        new File("Spectrum_1000.txt"), 
        new File("Spectrum_999.txt"), 
        new File("Spectrum_9990.txt"), 
        new File("Spectrum_9991.txt"), 
    };

    @Test
    public void sortByNumber() {
        Arrays.sort(files, new Comparator<File>() {
            @Override
            public int compare(File o1, File o2) {
                int n1 = extractNumber(o1.getName());
                int n2 = extractNumber(o2.getName());
                return n1 - n2;
            }

            private int extractNumber(String name) {
                int i = 0;
                try {
                    int s = name.indexOf('_')+1;
                    int e = name.lastIndexOf('.');
                    String number = name.substring(s, e);
                    i = Integer.parseInt(number);
                } catch(Exception e) {
                    i = 0; // if filename does not match the format
                           // then default to 0
                }
                return i;
            }
        });

        for(File f : files) {
            System.out.println(f.getName());
        }
    }
}

输出

Spectrum_1.txt
Spectrum_2.txt
Spectrum_7.txt
Spectrum_14.txt
Spectrum_999.txt
Spectrum_1000.txt
Spectrum_9990.txt
Spectrum_9991.txt

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