How to replace a CSV file after removing a column in Java

Question

I am new to Java. I was successfully able to read my CSV file from my local file location and was able to identify which column needed to be deleted for my requirements. However, I was not able to delete the required column and write the file into my local folder. Is there a way to resolve this issue? I have used the following code:

    CSVReader reader = new CSVReader(new FileReader(fileName));
    String [] nextLine;
    while ((nextLine = reader.readNext()) != null) {
        System.out.println(nextLine[15]);
    }

All I would like to do is to remove the column having index 15 and write the file as a CSV file in my local folder.

Hobojo · Accepted Answer · 2022-07-06 21:18:38Z

1

I'm assuming you're using the OpenCSV library.

In order to make your code work, you have to fix 2 issues:

You need a writer to write your modified CSV to. OpenCSV provides a CSVWriter class for this purpose.
You need to convert your line (which is currently a String array) into a list to be able to remove an element, then convert it back into an array to match what the CSVWriter.writeNext method expects.

Here's some code that does this:

CSVReader reader = new CSVReader(new FileReader(fileName));
CSVWriter writer = new CSVWriter(new FileWriter(outFileName));
String[] origLine;
while ((origLine = reader.readNext()) != null) {
    List<String> lineList = new ArrayList<>(Arrays.asList(origLine));
    lineList.remove(15);
    String[] newLine = lineList.toArray(new String[lineList.size()]);
    writer.writeNext(newLine, true);
}
writer.close();
reader.close();

Some additional remarks:

The code probably needs a bit more error handling etc if it's to be used in a production capacity.
List indices in Java start at 0, so remove[15] actually removes the 16th column from the file.
The code writes its output to a separate file. Trying to use the same file name for input and output will not work.

answered Jul 6, 2022 at 21:18

Hobojo

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3 Comments

DevilsHnd - 退した Over a year ago

"Trying to use the same file name for input and output will not work." Will it not work if the output destination was in a different directory?

David Conrad Over a year ago

@DevilsHnd C:\one\file.csv is a different file name than C:\two\file.csv

DevilsHnd - 退した Over a year ago

No, the file name (file.csv) is exactly the same. It's the path (C:\two\ ) to that file that is different.

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