java - 基于列对行进行排序

Question

有什么方法可以根据列进行排序吗？

我有这样的线条，

1000 Australia     Kangaroo            Canberra
1002 India         Tiger               Delhi
1092 Germany       Eagle               Berlin

以上行必须根据第二列进行排序，即澳大利亚、德国、印度。

所以，结果应该是，

1000 Australia     Kangaroo            Canberra
1092 Germany       Eagle               Berlin   
1002 India         Tiger               Delhi

数据来自文本文件

Answer 1

我建议使用 aTreeSet并阅读您的文本文件，并将您的数据保存在实现Comparable. 这样，当您添加数据时TreeSet，数据将以排序顺序添加。

此示例可能会有所帮助：

class Data implements Comparable<Data>{

    private int digits;
    private String country;
    private String animal;
    private String capital;

    public Data(int digits, String country, String animal, String capital){
        this.digits = digits;
        this.country = country;
        this.animal = animal;
        this.capital = capital;
    }

    public int getDigits() {
        return digits;
    }

    public void setDigits(int digits) {
        this.digits = digits;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }

    public String getAnimal() {
        return animal;
    }

    public void setAnimal(String animal) {
        this.animal = animal;
    }

    public String getCapital() {
        return capital;
    }

    public void setCapital(String capital) {
        this.capital = capital;
    }

    @Override
    public int compareTo(Data data) {
        return getCountry().compareTo(data.getCountry());
    }
}


class TestCountry{
    public static void main(String[] args) {
        TreeSet<Data> set = new TreeSet<Data>();
        /** 
         * Assuming that you can read the CSV file and build up the Data objects.
         * You would then put them in the set where they will be added in a sorted
         * fashion 
         */
        set.add(new Data(1000, "Australia", "Kangaroo", "Canberra"));
        set.add(new Data(1002, "India", "Tiger", "Delhi"));
        set.add(new Data(1092, "Germany", "Eagle", "Berlin"));

        for(Data data: set){
            System.out.println(data.getDigits()+"\t"+data.getCountry()+"\t"+data.getAnimal()+"\t"+data.getCapital());
        }
    }
}

Answer 2

您可以将数据构建为此模型

Row Class表示行数据

public class Row implements Comparable<Row> {

private int number;
private String country;
private String animal;
private String city;

public Row(int number, String country, String animal, String city) {
    super();
    this.number = number;
    this.country = country;
    this.animal = animal;
    this.city = city;
}

public int getNumber() {
    return number;
}

public void setNumber(int number) {
    this.number = number;
}

public String getCountry() {
    return country;
}

public void setCountry(String country) {
    this.country = country;
}

public String getAnimal() {
    return animal;
}

public void setAnimal(String animal) {
    this.animal = animal;
}

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
}

// Easy to print and show the row data
@Override
public String toString() {
    return "Row [number=" + number + ", country=" + country + ", animal="
            + animal + ", city=" + city + "]";
}

// sort based on column "country"
@Override
public int compareTo(Row o) {
    return this.country.compareTo(o.country);
}

}

并且测试示例将是

public static void main(String[] args) {

    ArrayList<Row> data = new ArrayList<Row>();
    data.add(new Row(1000, "Australia", "Kangaroo", "Canberra"));
    data.add(new Row(1002, "India", "Tiger", "Delhi"));
    data.add(new Row(1092, "Germany", "Eagle", "Berlin"));

    // To sort the data (based on column "country")
    Collections.sort(data);

    // Print and show the data
    for (int i = 0; i < data.size(); i++) {
        System.out.println(data.get(i));
    }


}

Answer 3

我建议您逐行阅读该文件并在每一行上使用 StringTokenizer 来访问单个单词。然后，您可以将每一行放入以国家为键的 HashMap 中。

使用

Collection<String> k = yourHashMap.keySet();
Collections.sort(k);

将按自然顺序对您的密钥集进行排序。然后，您可以遍历键集并以排序方式访问哈希图中的每一行。