Java 循环遍历每个唯一值

Question

我有一个像这样的 csv 文件:

"user1","track1","player1"
-------------------------
"user1","track2","player2"
-------------------------
"user1","track3","player3"
-------------------------
"user1","track4","player4"
-------------------------
"user2","track2","player3"
-------------------------
.
.
"userN","trackM","playerX"

我需要做的是将与每个用户相关的轨道和播放器分成两半，并将它们放在单独的文件中。例如，对于 user1，如果它有 4 行，我需要将其分为两部分(文件 A 中的前两行，文件 B 中的其余行)，并对所有用户重复相同的操作。这是我到目前为止所写的:

public static void main(String[] args) throws java.lang.Exception { 

    BufferedReader userlines = new BufferedReader(new FileReader("/Users/mona/Documents/Bolzano/Datasets/Lastfm_Matthias/lastfm_usertrackplayer.csv"));       
    String uLine = null;

    while ((uLine = userlines.readLine()) != null) {

        String[] userId = uLine.split(","); 
        ArrayList<String> list = new ArrayList<String>();       
        list.add(uLine);

    for(int i=0; i<=list.size();i++){       
    //  --> THIS FOR CONDITION IS MY PROBLEM,I need s.th like for(i=0; i<=(last unique userId (i.e., length of userId[i]) until it reaches the next unique userId)      
          //Divide the lines and put into two separate files           

            }
    }
    userlines.close();
}

抱歉，我知道这应该很简单，但我确实无法通过谷歌搜索我的问题找到任何相关/类似的问题:(有人可以帮我吗？

谢谢

Answer 1

您无法“先验”知道每个用户的行数。因此，您必须记住(例如在列表中)当前用户的所有行，直到读取下一个用户为止。然后在这两个文件中保存列表的内容。

清理列表，为下一个用户执行相同的操作。

编辑

public static void main(String[] args) throws java.lang.Exception { 

    try(BufferedReader userlines = new BufferedReader(new FileReader("/Users/mona/Documents/Bolzano/Datasets/Lastfm_Matthias/lastfm_usertrackplayer.csv"));) {       
    String uLine = null;

    ArrayList<String> list = new ArrayList<String>();  
    String currentUserId = null;     
    while ((uLine = userlines.readLine()) != null) {

        String[] userData = uLine.split(","); 
        String userId = userData[0]; // <-- get User ID here
        if (userId.equals(currentUserId)) {
            // Do what ever you need while buffering same userId
        } else {
            // Save currentUserId in file
            yourSaveMethod(list);
            currentUserId = userId;
            list.clear();
        }
        list.add(uLine);

        }
    }
}