adding multiple columns to a csv file

Question

Here is my existing csv file:

userid,name
1,Jim
2,Sally
3,Bob

I can add another column using CsvMapReader/Writer and make it look like:

userid,name,time
1,Jim,64913824823208
2,Sally,64913824900056
3,Bob,64913824966956

However, if I want to add another column to make my csv look something like:

userid,name,time,day
1,Jim,64913824823208,Mon
2,Sally,64913824900056,Mon
3,Bob,64913824966956,Mon

How do I achieve this?

The code segment I used to add a column is:

CsvPreference prefs = CsvPreference.STANDARD_PREFERENCE;
mapReader = new CsvMapReader(new FileReader(path+csvFileName), prefs);
mapWriter = new CsvMapWriter(new FileWriter(path+desiredFileNameWithDateOfPull), prefs);

// header used to read the original file
final String[] readHeader = mapReader.getHeader(true);

// header used to write the new file 
// (same as 'readHeader', but with additional column)
final String[] writeHeader = new String[readHeader.length + 1];
System.arraycopy(readHeader, 0, writeHeader, 0, readHeader.length);
final String str= "day";
writeHeader[writeHeader.length - 1] = str;

mapWriter.writeHeader(writeHeader);
Map<String, String> row;
while( (row = mapReader.read(readHeader)) != null ) {
  // add your column with desired value
  row.put(str, "Mon");
  mapWriter.write(row, writeHeader);
}

I don't see where is the problem. You were already able to add a column using CsvMapWriter. To add another one I'd suggest to do step 1 again ;). — David Guyon, Feb 16 '16 at 07:30
I tried to put step 1 in a loop. It didn't work out. So I had to repeat the code with different variables. Repeating the code is tolerable for say 3 or 4 more columns. But what if I need to add, say, 20 or 30 more columns? That's why I need a method in which I can loop the process of step 1 (just to make it more efficient) :) — khalibali, Feb 16 '16 at 10:39

score 0 · Answer 1 · answered Feb 16 '21 at 18:18

public static void main(String[] args) throws IOException {

    ICsvMapReader mapReader = null;
    ICsvMapWriter mapWriter = null;
    try {
        CsvPreference prefs = CsvPreference.STANDARD_PREFERENCE;
        mapReader = new CsvMapReader(new FileReader("input.csv"), prefs);
        mapWriter = new CsvMapWriter(new FileWriter("output.csv"), prefs);

        // header used to read the original file
        final String[] readHeader = mapReader.getHeader(true);

        // header used to write the new file 
        // (same as 'readHeader', but with additional column)
        final String[] writeHeader = new String[readHeader.length + 2];
        System.arraycopy(readHeader, 0, writeHeader, 0, readHeader.length);
        final String timeHeader = "time";
        final String str="day";
        writeHeader[writeHeader.length - 2] = timeHeader;
        writeHeader[writeHeader.length-1]= str;

        mapWriter.writeHeader(writeHeader);

        Map<String, String> row;
        while( (row = mapReader.read(readHeader)) != null ) {

            // add your column with desired value
            row.put(timeHeader, String.valueOf(System.nanoTime()));
            row.put(str,"mon");

            mapWriter.write(row, writeHeader);
        }

    }
    finally {
        if( mapReader != null ) {
            mapReader.close();
        }
        if( mapWriter != null ) {
            mapWriter.close();
        }
    }

I experimented alot and it worked for me. I used similar code to store the result value in the csv file. Hope it helps. — Sahithi Reddy, Feb 16 '21 at 18:19

adding multiple columns to a csv file

1 Answers1