List of List<String> to string ordered string array

Question

I am having a resultList which is a string list were each element in this list is also a List<String>. Now I want to put my data into a csv sheet. For that I am using opencsv.

    List<String[]> data = new ArrayList<String[]>();
    for(int m = 0; m < resultList.get(0).size(); m++) {
        for (int i = 0; i < resultList.size(); i++) {

            data.add(new String[] {resultList.get(i).get(m).toString()});

        }
    }

    writer.writeAll(data);

    //close Writer
    writer.close();

My data should look like that:

enter image description here

However, my implementation gives me that:

enter image description here

In my implementation I am taking, knowing that every sublist has the same length, from each sublist the first element and add it to the array. Why am I getting this long row?

I appreciate your replies!

@Dukeling Can you recommend any code structure?

user2051347
– user2051347

2014-02-07 08:38:00 +00:00
Commented Feb 7, 2014 at 8:38 — user2051347
– user2051347, Commented Feb 7, 2014 at 8:38

Weibo Li · Accepted Answer · 2014-02-07 10:32:34Z

1

Because your loop is incorrect. You constructed a new String array in every inner loop, so every array has only on element. Try the following code:

List<String[]> data = new ArrayList<String[]>();
for(List<String> strlist : resultList) {

    String[] array = new String[strlist.size()];
    int offset = 0;
    for(String s : strlist) {
        array[offset ++] = s;
    }
    data.add(array);
}

============== Edited bellow ==================

I've re-ordered the loop to match your output requirement. Also, a sample input is provided to test the algorithm.

List<List<String>> resultList = new ArrayList<List<String>>();
for (int i = 1; i <= 9; i++) {

    List<String> innerList = new ArrayList<String>();
    resultList.add(innerList);
    for (int j = 1; j <= 9; j++) {
        innerList.add(j + "");
    }
}

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

for(int m = 0; m < resultList.get(0).size(); m++) {

    String[] array = new String[resultList.size()];
    for (int i = 0; i < resultList.size(); i++) {
        array[i] = resultList.get(i).get(m).toString();
    }
    data.add(array);
}
for(String[] array : data) {
    System.out.println(Arrays.toString(array));
}

edited Feb 7, 2014 at 10:32

answered Feb 7, 2014 at 8:29

Weibo Li

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4 Comments

Weibo Li Over a year ago

@user2051347: I forgot data.add(array);, sorry for that. I've corrected my code.

user2051347 Over a year ago

Thx for your reply! However what I am currently getting is the resuls column wise and not row by row. Any suggestions how that can be fixed? I really would appreciate your reply!!!

Weibo Li Over a year ago

@user2051347: Please give me a sample input of resultList, and expected output. I'll change the loop order to match your request.

user2051347 Over a year ago

Thx for your help! Sample input would be to have 3 string lists with the numbers 1 to 9 and then give them out that each row has the numbers 1 to 9(as it can be seen on the first picture). I really appreciate your help!

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