Question

i dont’t use java very often and now i got some Problem.
I want to read a CSV file like this one:

A,B,C,D
A,B,F,K
E,F,S,A
A,B,C,S
A,C,C,S

Java don’t know dynamic arrays, so i choose an ArrayList. This works so far. The Problem is:
How can I store the ArrayList? I think an other ArrayList would help.
This is what I got:

    BufferedReader reader = new BufferedReader(
            new InputStreamReader(this.getClass().getResourceAsStream(
                    "../data/" + filename + ".csv")));

    List rows = new ArrayList(); 

    String line;
    while ((line = reader.readLine()) != null) {

        rows.add(Arrays.asList(line.split(",")));

    }

Now I get an ArrayList with a size of 5 for rows.size().
How do I get row[0][0] for example?

What do I want to do? The Problem is i want to find the same row except the last column.
For example i want to find row 0 and row 3.
thank you very much

Thank you all! You helped me a lot. =) Maybe Java and I will become friends =) THANKS!

Answer 1

You don’t need to know the row size in advance, String.split() returns a String array:

List<String[]> rows = new ArrayList<String[]>(); 

String line = null;
while((line = reader.readLine()) != null)
    rows.add(line.split(",", -1));

To access a specific row:

int len = rows.get(0).length;
String val = rows.get(0)[0];

Also, are you always comparing by the entire row except the last column? You could just take off the last value (line.replaceFirst(",.*?$", "")) and compare the rows as strings (have to be careful of whitespace and other formatting, of course).

A slightly different way:

Set<String> rows = new HashSet<String>(); 

String line = null;
while((line = reader.readLine()) != null){
    if(!rows.add(line.substring(0, line.lastIndexOf(','))))
        System.out.println("duplicate found: " + line);
}

Of course, modify as necessary if you actually need to capture the matching lines.