Java append new column to csv file

Question

I want to calculate some column data and write it to csv file as column. Then after calculating other column of data I want to append it to same file but as new column.

Here is what I did:

try {
    FileWriter writer = new FileWriter(OUT_FILE_PATH, true);
    for (int i=0; i<data.size(); i++) {
        writer.append(String.valueOf(data.get(i)));
        writer.append(",");
        writer.append("\n");
    }
    writer.flush();
    writer.close();
} catch (Exception e) {}

Result - It appends the new column below the first column, so I have single long column.

Thanks,

What do you use the \n for? That might cause these problems. — LordAnomander
– LordAnomander, Commented Jan 4, 2016 at 12:17
I don't know your data structure, but if you know the number of columns, you could use two loops, i.e., a for-loop for each row and use \n after a row is finished. — LordAnomander
– LordAnomander, Commented Jan 4, 2016 at 12:20
@tbrown as i mentioned the data structure is simple: every time I call this method I have single column of simple integers I need to put inside. Every call to this method I know only 1 column a time. — michael
– michael, Commented Jan 4, 2016 at 12:22

Pang · Accepted Answer · 2017-05-25 10:14:53Z

4

Something like this perhaps:

public void appendCol(String fileName, ???ArrayList??? data) { //assuming data is of type ArrayList here, you need to be more explicit when posting code

    String lineSep = System.getProperty("line.separator");
    String output = "";
    try{
        BufferedReader br = new BufferedReader(new  FileReader(fileName));
        String line = null;
        int i = 0;
        while ((line = br.readLine()) != null) {
            output += line.replace(
                    lineSep,
                    "," + String.valueOf(data.get(i)) + lineSep);
            i++;
        }
        br.close();
        FileWriter fw = new FileWriter(fileName, false); //false to replace file contents, your code has true for append to file contents
        fw.write(output);
        fw.flush();
        fw.close();
    } catch (Exception e){
        e.printStackTrace();
    } 
}

edited May 25, 2017 at 10:14

Pang

10.2k146 gold badges87 silver badges126 bronze badges

answered Jan 4, 2016 at 13:17

Fin

1831 silver badge6 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

dsp_user · Accepted Answer · 2016-01-04 12:34:03Z

2

You will have to read your file (line by line) and then insert the new column to every line. Here's a solution using BufferedReader and BufferedWriter

public void addColumn(String path,String fileName) throws IOException{
    BufferedReader br=null;
    BufferedWriter bw=null;
    final String lineSep=System.getProperty("line.separator");

    try {
        File file = new File(path, fileName);
        File file2 = new File(path, fileName+".1");//so the
                    //names don't conflict or just use different folders

        br = new BufferedReader(new InputStreamReader(new FileInputStream(file))) ;
        bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file2)));
        String line = null;
                    int i=0;
        for ( line = br.readLine(); line != null; line = br.readLine(),i++)
        {               

            String addedColumn = String.valueOf(data.get(i));
            bw.write(line+addedColumn+lineSep);
    }

    }catch(Exception e){
        System.out.println(e);
    }finally  {
        if(br!=null)
            br.close();
        if(bw!=null)
            bw.close();
    }

}

edited Jan 4, 2016 at 12:34

answered Jan 4, 2016 at 12:25

dsp_user

2,1332 gold badges18 silver badges27 bronze badges

4 Comments

michael Over a year ago

Basically you suggest every time to write to a new file - tmp file, and in the end append to the final file containing all other good columns?

dsp_user Over a year ago

Or just delete the old file and rename the new file to the original name.

michael Over a year ago

yes I got it, it works, need to change line+addedColumn+lineSep to line+","+addedColumn+lineSep

CalebKing3 Over a year ago

What is data in this example? Is it suppose to be a CSV file?

Dasari Swaroop Kumar · Accepted Answer · 2021-02-17 19:22:01Z

I have used apache-commons for resolving this issue. There was no perfect answer that worked for me. After a lot of effort, this worked for me.

Writer writer = Files.newBufferedWriter(Paths.get("output.csv"));
        CSVPrinter csvPrinter = new CSVPrinter(writer, CSVFormat.DEFAULT
//add whichever column you want in withHeader
                .withHeader("createdTs", "destroyedTs", "channelName", "uid", "suid", "did", "joinTs", "leaveTs", "platform", "location", "consumption"));

//actual columns in your passed CSV
 String[] HEADERS = {"createdTs", "destroyedTs",    "channelName", "uid", "suid", "did", "joinTs", "leaveTs", "platform", "location"};
    Reader in = new FileReader(yourCsvFile);
    Iterable<CSVRecord> records = CSVFormat.DEFAULT
            .withHeader(HEADERS)
            .withFirstRecordAsHeader()
            .parse(in);

    for (CSVRecord row : records) {
        String tempValue = String.valueOf(Long.parseLong(row.get("leaveTs")) - Long.parseLong(row.get("joinTs")));
        csvPrinter.printRecord(row.get("createdTs"), row.get("destroyedTs"),row.get("channelName"), row.get("uid"),
                                 row.get("suid"), row.get("did"), row.get("joinTs"), row.get("leaveTs"),
                                 row.get("platform"), row.get("location"), tempValue);
    }

Pang · Accepted Answer · 2017-05-25 10:14:30Z

-1

Hope this will help you.

{
    //CREATE CSV FILE 
    StringBuffer csvReport = new StringBuffer(); 
    csvReport.append("header1,Header2,Header3\n"); 
    csvReport.append(value1 + "," + value2 + "," + value3 + "\n"); 

    generateCSVFile( filepath,fileName, csvReport); // Call the implemented mathod 
}

public void generateCSVFile(String filepath,String fileName,StringBuffer result)
{
    try{

    FileOutputStream fop = new FileOutputStream(filepath);

    // get the content in bytes
    byte[] contentInBytes = result.toString().getBytes();

    fop.write(contentInBytes);
    fop.flush();

    //wb.write(fileOut);
    if(fop != null)
        fop.close();
    }catch (Exception ex)
    {
        ex.printStackTrace();
    }
}

edited May 25, 2017 at 10:14

Pang

10.2k146 gold badges87 silver badges126 bronze badges

answered Jan 4, 2016 at 13:11

Doss

573 bronze badges

2 Comments

Serg Shapoval Over a year ago

bad answer. but what he gona do if he wants to write to file not line by line but column by column?

kerner1000 Over a year ago

you just copy the file bytes. For what should that be useful? Not an answer to the question.

Collectives™ on Stack Overflow

Java append new column to csv file

4 Answers 4

Comments

4 Comments

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

4 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related