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[英]Java: Most efficient way to loop through CSV and sum values of one column for each unique value in another Column
[英]Java loop through each unique value
我有这样的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曲目和播放器分成两半,并将它们放在单独的文件中。 例如,对于user1,如果它有4行,则需要将其分为两部分(文件A中的前两行,文件B中的其余两行),并对所有用户重复相同的操作。 这是我到目前为止写的:
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,但是通过搜索我的问题我真的找不到任何相关/相似的问题:(有人可以帮我吗?
谢谢
您无法知道“先验”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,直到您读取下一个用户。 然后在两个文件中保存列表的内容。
清理列表,对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);
}
}
}
您可以使用StringTokenizer class
来解析数据。
例:
String str = "user1, track1, player1";
StringTokenizer st = new StringTokenizer(str);
System.out.println("---- Split by space ------");
while (st.hasMoreElements()) {
System.out.println(st.nextElement());
}
System.out.println("---- Split by comma ',' ------");
StringTokenizer st2 = new StringTokenizer(str, ",");
while (st2.hasMoreElements()) {
System.out.println(st2.nextElement());
}
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