如何在Java中按两列对csv文件进行排序? [英] How to sort csv file by two columns in java?

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问题描述

如何按两列对CSV文件进行排序?现在，我可以按一列对其进行排序.我需要按前两列对其进行排序.怎么做?这是我用来按其第一列对其进行排序的代码:

How to sort CSV file by two columns? Right now I am able to sort it by one column. I need to sort it by first two columns. How to do it? Here is the code that I am using for sorting it by its first column:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

public class Practice {
    public static void main(String[] args) throws Exception {
        BufferedReader reader = new BufferedReader(new FileReader("sample-input.csv"));
        Map<String, List<String>> map = new TreeMap<String, List<String>>();
        String line = reader.readLine();//read header
        while ((line = reader.readLine()) != null) {
            String key = getField(line);
            List<String> l = map.get(key);
            if (l == null) {
                l = new LinkedList<String>();
                map.put(key, l);
            }
            l.add(line);
        }

        reader.close();
        FileWriter writer = new FileWriter("output.csv");
        writer.write("Symbol, Exchange, Minimum, Average, Maximum, Total\n");
        for (List<String> list : map.values()) {
            for (String val : list) {
                writer.write(val);
                writer.write("\n");
            }
        }
        writer.close();
    }

    private static String getField(String line) {
        return line.split(",")[0];
        // extract value you want to sort on
    }
}

两列排序后的输出如下:

The output after two column sort becomes like:

ABC,X,0.10,10
ABC,X,0.09,20
ABC,X,0.11,10
ABC,X,0.11,20
ABC,X,0.10,10
ABC,Y,0.09,10
ABC,Y,0.08,10
ABC,Z,0.12,15
ABC,Z,0.10,15
DEF,X,0.17,10
DEF,X,0.14,10
DEF,Y,0.15,15
DEF,Y,0.15,15
DEF,Y,0.17,15
DEF,Y,0.16,15
DEF,Y,0.17,15
DEF,Z,0.14,10
DEF,Z,0.15,10

我需要这样的输出:

ABC,X,0.09,0.11
ABC,X,0.09,0.11
ABC,X,0.09,0.11
ABC,X,0.09,0.11
ABC,X,0.09,0.11
ABC,Y,0.08,0.9
ABC,Y,0.08,0.9
ABC,Z,0.10,0.12
ABC,Z,0.10,0.12
DEF,X,0.14,0.17
DEF,X,0.14,0.17
DEF,Y,0.15,0.17
DEF,Y,0.15,0.17
DEF,Y,0.15,0.17
DEF,Y,0.15,0.17
DEF,Y,0.15,0.17
DEF,Z,0.14,0.15
DEF,Z,0.14,0.15

但是，我希望第三列显示X的最小值，然后显示Y的最小值，然后显示第三列中当前显示的值的Z.

But, I want the third column to display the minimum of the values for X, then min value for Y, and then Z from the values that are currently being displayed in the third column.

推荐答案

尽管创建类作为域的适当表示形式通常是一个好主意:在这种情况下，我 不同意

Although it's often a good idea to create classes that serve as appropriate representations for the domain: In this case, I disagree with the comments.

读取CSV并按一列或多列(的String内容)对其进行排序是非常通用的操作.并且它独立于域.

Reading a CSV and sorting it by (the String contents of) one or more columns is a very generic operation. And it is independent of the domain.

可以实现Comparator，该Comparator只是在List<String>的多个索引处选择字符串，然后按字典顺序比较这些索引处的值.使用此Comparator，可以对从CSV文件读取的任何List<List<String>>进行排序.

It is possible to implement a Comparator that simply picks the strings at several indices of a List<String>, and compares the values at these indices lexicographically. With this Comparator, one can sort any List<List<String>> that was read from a CSV file.

这是一个简单的例子.可用于根据任意列的字符串内容对任何 CSV文件进行排序.

Here is a simple example. It can be used to sort any CSV file based on the string contents of arbitrary columns.

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class MultiColumnCsvSort
{
    private static final String COLUMN_SEPARATOR = ",";

    public static void main(String[] args) throws Exception
    {
        InputStream inputStream = new FileInputStream("sample-input.csv");
        List<List<String>> lines = readCsv(inputStream);

        // Create a comparator that sorts primarily by column 0,
        // and if these values are equal, by column 2
        Comparator<List<String>> comparator = createComparator(0, 2);
        Collections.sort(lines, comparator);

        OutputStream outputStream = new FileOutputStream("output.csv");
        String header = "Symbol, Exchange, Minimum, Average, Maximum, Total";
        writeCsv(header, lines, outputStream);        
    }

    private static List<List<String>> readCsv(
        InputStream inputStream) throws IOException
    {
        BufferedReader reader = new BufferedReader(
            new InputStreamReader(inputStream));
        List<List<String>> lines = new ArrayList<List<String>>();

        // Skip header
        String line = reader.readLine();

        while (true)
        {
            line = reader.readLine();
            if (line == null)
            {
                break;
            }
            List<String> list = Arrays.asList(line.split(COLUMN_SEPARATOR));
            lines.add(list);
        }
        return lines;
    }

    private static void writeCsv(
        String header, List<List<String>> lines, OutputStream outputStream) 
        throws IOException
    {
        Writer writer = new OutputStreamWriter(outputStream);
        writer.write(header+"\n");
        for (List<String> list : lines)
        {
            for (int i = 0; i < list.size(); i++)
            {
                writer.write(list.get(i));
                if (i < list.size() - 1)
                {
                    writer.write(COLUMN_SEPARATOR);
                }
            }
            writer.write("\n");
        }
        writer.close();

    }

    private static <T extends Comparable<? super T>> Comparator<List<T>> 
        createComparator(int... indices)
    {
        return createComparator(MultiColumnCsvSort.<T>naturalOrder(), indices);
    }

    private static <T extends Comparable<? super T>> Comparator<T>
        naturalOrder()
    {
        return new Comparator<T>()
        {
            @Override
            public int compare(T t0, T t1)
            {
                return t0.compareTo(t1);
            }
        };
    }

    private static <T> Comparator<List<T>> createComparator(
        final Comparator<? super T> delegate, final int... indices)
    {
        return new Comparator<List<T>>()
        {
            @Override
            public int compare(List<T> list0, List<T> list1)
            {
                for (int i = 0; i < indices.length; i++)
                {
                    T element0 = list0.get(indices[i]);
                    T element1 = list1.get(indices[i]);
                    int n = delegate.compare(element0, element1);
                    if (n != 0)
                    {
                        return n;
                    }
                }
                return 0;
            }
        };
    }
}

几年后更新:

Updated a few years later:

如果您想在各个列的排序顺序方面具有更大的灵活性，可以使用不同的选项.哪一个是最佳"，很大程度上取决于您要如何组装"实际的比较器-也就是说，您要如何定义哪个列应在哪个订单.但是，这里显示了一个简单的示例:

If you want more flexibility regarding the sort order of individual columns, there are different options. Which one is the "best" one largely depends on how you want to "assemble" the actual comparator - that is, how you want to define which column should be sorted in which order. But one simple example is shown here:

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class MultiColumnCsvSortExtended
{
    private static final String COLUMN_SEPARATOR = ",";

    public static void main(String[] args) throws Exception
    {
        InputStream inputStream = new FileInputStream("sample-input.csv");
        List<List<String>> lines = readCsv(inputStream);

        // Create a comparator that compares the elements from column 0,
        // in ascending order
        Comparator<List<String>> c0 = createAscendingComparator(0);

        // Create a comparator that compares the elements from column 2,
        // in descending order
        Comparator<List<String>> c1 = createDesendingComparator(2);

        // Create a comparator that compares primarily by using c0,
        // and secondarily by using c1
        Comparator<List<String>> comparator = createComparator(c0, c1);
        Collections.sort(lines, comparator);

        OutputStream outputStream = new FileOutputStream("output.csv");
        String header = "Symbol, Exchange, Minimum, Average";
        writeCsv(header, lines, outputStream);        
    }

    private static List<List<String>> readCsv(
        InputStream inputStream) throws IOException
    {
        BufferedReader reader = new BufferedReader(
            new InputStreamReader(inputStream));
        List<List<String>> lines = new ArrayList<List<String>>();

        String line = null;

        // Skip header
        line = reader.readLine();

        while (true)
        {
            line = reader.readLine();
            if (line == null)
            {
                break;
            }
            List<String> list = Arrays.asList(line.split(COLUMN_SEPARATOR));
            lines.add(list);
        }
        return lines;
    }

    private static void writeCsv(
        String header, List<List<String>> lines, OutputStream outputStream) 
        throws IOException
    {
        Writer writer = new OutputStreamWriter(outputStream);
        writer.write(header+"\n");
        for (List<String> list : lines)
        {
            for (int i = 0; i < list.size(); i++)
            {
                writer.write(list.get(i));
                if (i < list.size() - 1)
                {
                    writer.write(COLUMN_SEPARATOR);
                }
            }
            writer.write("\n");
        }
        writer.close();

    }

    @SafeVarargs
    private static <T> Comparator<T>
        createComparator(Comparator<? super T>... delegates)
    {
        return (t0, t1) -> 
        {
            for (Comparator<? super T> delegate : delegates)
            {
                int n = delegate.compare(t0, t1);
                if (n != 0)
                {
                    return n;
                }
            }
            return 0;
        };
    }

    private static <T extends Comparable<? super T>> Comparator<List<T>>
        createAscendingComparator(int index)
    {
        return createListAtIndexComparator(Comparator.naturalOrder(), index);
    }

    private static <T extends Comparable<? super T>> Comparator<List<T>>
        createDesendingComparator(int index)
    {
        return createListAtIndexComparator(Comparator.reverseOrder(), index);
    }

    private static <T> Comparator<List<T>>
        createListAtIndexComparator(Comparator<? super T> delegate, int index)
    {
        return (list0, list1) -> 
            delegate.compare(list0.get(index), list1.get(index));
    }

}

这篇关于如何在Java中按两列对csv文件进行排序?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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