Java modify csv line

Question

I want to remove the the 2nd and 3rd column from a csv file but don't know how to. My current code is like this:

BufferedReader br = new BufferedReader(new FileReader(dir + file));
BufferedWriter bw = new BufferedWriter(new FileWriter(target + file));

String perLine;
while ((perLine = br.readLine()) != null) {

    Code to remove the 2nd and 3rd column...

    bw.write(perLine)
}
br.close();
bw.close();

Data is something like this:

1,abc,2,def,data,data,1,2,3,4,5
2,wxyz,32,abc,data,data,1,2,3,4,5

Want to achieve this:

1,def,data,data,1,2,3,4,5
2,abc,data,data,1,2,3,4,5

Is this possible without adding any csv lib or just doing regex? anyone can give me an idea or example?

try using net.sf.opencsv jar

Scary Wombat
– Scary Wombat

2014-12-12 00:48:20 +00:00
Commented Dec 12, 2014 at 0:48 — Scary Wombat
– Scary Wombat, Commented Dec 12, 2014 at 0:48

Community · Accepted Answer · 2021-10-07 05:59:28Z

3

It is fairly simple to do as long as you take the "CSV is lines with fields between commas" approach. The problem is the fact that CSV is actually a fair bit more complicated than that; when you take into account things can get quoted, quotes can get escaped, and quoted fields can contain newlines... then it's not easily parsable using regexps. Thus, whenever you need to support standard CSV (for example, as specified in RFC4180, you really really want to use a library, and not cook your own solution.

That said...

You can't change the current file. The way to do it would be to either read the file, change the contents, then write it back, or while reading the file write to another (temporary) file, then switch.

The part about removing 2nd and 3rd columns, in the naive approach:

String fields[] = perLine.split(",");
String newFields[] = new String[fields.length - 2];
newFields[0] = fields[0];
System.arrayCopy(fields, 3, newFields, 1, fields.length - 1);

edited Oct 7, 2021 at 5:59

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answered Dec 12, 2014 at 0:50

Amadan

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1 Comment

Asaph Over a year ago

Change perLine.split(',') to perLine.split(","). String#split() accepts a String, not a char.

Community · Accepted Answer · 2021-10-07 06:15:07Z

1

There are a lot of nuances when dealing with CSVs that follow RFC4180. There are things to take into consideration such as quoted strings, escaped quoted strings, commas in those, multi line fields, and many others. Some more of those can be found here.

If you can make the assumption that the data is just "between the commas", and not about dealing with all valid CSV, you could split the string on , and omit the indices you don't want.

Here is an example of excluding those indices and using Java 8's String.join to form the output string:

String[] split = test.split(",");
String[] outputFields = new String[split.length - 2];
outputFields[0] = split[0];
System.arraycopy(split, 3, outputFields, 1, split.length - 3);

String result = String.join(",", outputFields);

edited Oct 7, 2021 at 6:15

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answered Dec 12, 2014 at 0:57

mkobit

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Comments

Auli · Accepted Answer · 2014-12-12 01:50:00Z

Use opencsv



 CSVWriter writer = null;
    try {
        //Read file here.... 
        String str = "1,abc,2,def,data,data,1,2,3,4,5"; 
        writer = new CSVWriter(new FileWriter("test.csv"),',',CSVWriter.NO_QUOTE_CHARACTER); 
        String strArr[] = str.split(","); 
        List<String> output = new ArrayList<>(); 
        for (int i = 0; i < strArr.length; i++) { 
        if (i == 1 || i == 2) {
            continue;
        } else {
            output.add(strArr[i] );
        }
    }
    if(!output.isEmpty()){
        String[] array = new String[output.size()];
        writer.writeNext(output.toArray(array));
    }
 } finally {
    if (writer != null)
        writer.close();
    }

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