java - 阅读独特的值(value)观

Question

我编写了一段代码，用于从文本文件的列中读取值。为了输出值的数量，我使用了“长度”，效果很好......但我只需要计算唯一值的数量。

public class REading_Two_Files {

public static void main(String[] args) {

    try {
        readFile(new File("C:\\Users\\teiteie\\Desktop\\RECSYS\\yoochoose-test.csv"), 0,( "C:\\Users\\teiteie\\Desktop\\RECSYS\\yoochoose-buys.csv"), 3);
     //readFile(new File(File1,0, File2,3);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

////0 - 将打印 file1 中的列 //3 - 将打印文件 2 中的列

private static void readFile(File fin1,int whichcolumnFirstFile,String string,int whichcolumnSecondFile) throws IOException {
    //private static void readFile(File fin1,int whichcolumnFirstFile,String string,int whichcolumnSecondFile) throws IOException
    // code for this method.
    //open the two files.

    int noSessions = 0;
    int noItems = 0;
//  HashSet<String> uniqueLength = new HashSet<String>();


    FileInputStream fis = new FileInputStream(fin1); //first file
    FileInputStream sec = new FileInputStream(string); // second file

//Construct BufferedReader from InputStreamReader
    BufferedReader br1= new BufferedReader(new InputStreamReader(fis));
    BufferedReader br2= new BufferedReader(new InputStreamReader(sec));

    String lineFirst = null, first_file[];
    String lineSec = null, second_file [];

    while ((lineFirst = br1.readLine()) != null && (lineSec = br2.readLine()) != null) {
        first_file= lineFirst.split(",");
        second_file = lineSec.split(",");

        //int size = data[].size();

    System.out.println(first_file[0]+" , "+second_file[0]);



    if(first_file.length != 0){
        noSessions++;
        }

        if(second_file.length != 0)  {
        noItems ++;
        }



        }

        br1.close();
        br2.close();
        System.out.println("no of sessions "+noSessions+"\nno of items "+noItems );


    }


}

Answer 1

为了仅计算唯一值，我们通常使用 Set因为它们被指定为仅包含唯一值。

A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element. As implied by its name, this interface models the mathematical set abstraction.

本质上 - 将所有值放入 Set 中(通常 HashSet 是最有效的，但如果您想要并发性，有更好的选择)，然后采用 Set.size() 作为您输入的唯一值的数量。