Sort one column of data in a csv file in ascending order in java
Remove the new lines from data1.csv.
I would prefer to use the second generic String of the Map as a list of string and everything is almost same like below
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 Sort {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new FileReader("data1.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("sorted_numbers.txt");
writer.write("UserID, Module, Mark\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
}
}
Izzy
Updated on June 27, 2022Comments
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Izzy almost 2 years
import java.io.*; import java.util.*; public class Sort { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new FileReader("data1.csv")); Map<String, String> map=new TreeMap<String, String>(); String line=""; while((line=reader.readLine())!=null){ map.put(getField(line),line); } reader.close(); FileWriter writer = new FileWriter("sorted_numbers.txt"); for(String val : map.values()){ 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 } }
Hia I am trying to read a unsorted file and get Java to sort one column of the csv data file and print those results in a new file. I borrowed this solution whilst I was searching on this website because I think it is ideal for what I am trying to acomplish. I have a 282 rows of data in the form of
UserID, Module, Mark Ab004ui, g46PRo, 54 cb004ui, g46GRo, 94 gy004ui, g46GRo, 12 ab004ui, g46PRo, 34
this is in the csv file. when I use the above code it only gives me one line in the sorted_marks.txt, like this
ab004ui, g46PRo, 34
and I believe it wasnt even sorted.
I want all the results from the new file to be sorted based on their userID and nothing else but I can't seem to get it to work, please any help would be greatful
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Izzy over 14 yearsyey that works but for some reason it has made it a big block of results, like this: Ab004ui, g46PRo, 54, cb004ui, g46GRo, 94. rather then each result on indiviudal lines. so it should return it like: ab004ui, g46PRo, 34 cd004ui, G46PRo, 29
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Francis Upton IV over 14 yearsYou might want to repost your code. The code that's posted does seem to be writing a newline at the end of each row. Check that that's still there.
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Izzy over 14 yearsI edited my original post and added what you suggested, the comma. but not trim() string function, as I keep on getting error. I think I am not adding it right to the code. Also Map is overwriting the userID of the same type which is annoying, is anyway of stopping it from doing that?
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Izzy over 14 yearsThank you kindly for this, I have marked this as the answer, I am acutally going to get some reading done on maps, as this is a very interesting way of completing this problem. Now all I have to do is make it into a method and im done. Thanks again for all your help and explanations