Music.java

import java.io.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.stream.Collectors;

public class Main {

    public static final int MAX_PER_LINE = 6;
    public static final String FILE_IN = "C:\\Users\\denia\\Desktop\\val temps int.csv";
    public static final String FILE_OUT = "C:\\Users\\denia\\Desktop\\val temps int - Copie.csv";

    public static void main(String[] args) throws IOException {
        System.out.println("Loading dataset");
        List<String[]> dataset = loadDataset(FILE_IN);
        System.out.printf("Loaded %s rows", dataset.size());

        System.out.println("Processing rows...");
        Iterator<String[]> iterator = dataset.iterator();
        String[] last = iterator.next();
        int max = last.length;

        while(iterator.hasNext()){
            String[] current = iterator.next();

            //if time stamps are equal
            if(last[0].equals(current[0])){
                System.out.printf("Found duplicate '%s'\n", last[0]);
                iterator.remove();//remove line

                //find free index in last values and replace it
                for (int i = 2; i < last.length; i++) {
                    if(last[i] == null){
                        last[i] = current[1];//replace by new value
                        break;
                    }
                }
            }else{
                last = current;
                max = Math.max(max, current.length);
            }


        }

        //replace null
        System.out.println("Replacing empty cells...");
        int finalMax = max;
        dataset = dataset.stream().map(values -> {
           String[] newValues = new String[finalMax];

            for (int i = 0; i < finalMax; i++) {
                if(values[i] != null){
                    newValues[i] = values[i];
                }else{
                    newValues[i] = "S0";
                }
            }
           return newValues;
        }).collect(Collectors.toList());


        System.out.println("Saving result");

        writeDataset(dataset, FILE_OUT);

        System.out.println("Saved");
    }

    private static void writeDataset(List<String[]> dataset, String file) throws IOException {
        try(FileWriter fw = new FileWriter(file); BufferedWriter br = new BufferedWriter(fw)){
            for (String[] strings : dataset) {
                for (int i = 0; i < strings.length; i++) {
                    if(i != 0)br.append(',');
                    br.append(strings[i]);
                }
                br.append('\n');
            }
        }
    }

    private static List<String[]> loadDataset(String file) throws IOException {

        try (FileReader fr = new FileReader(file); BufferedReader br = new BufferedReader(fr)) {
            List<String[]> v = new ArrayList<>();

            String line;

            //load csv
            while ((line = br.readLine()) != null) {
                v.add(line.split(";"));
            }

            //extends arrays
            v = v.stream().map(values -> {
                String[] newValues = new String[MAX_PER_LINE];
                System.arraycopy(values,0,newValues, 0, values.length);
                return newValues;
            }).collect(Collectors.toList());
            return v;
        }
    }
}