[Solved] How to change data from long to wide form in Java

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Here’s a method that will reformat the data

This is assuming your data is {["Yes", "121", "1"], ...}

You may need some minor adjustments if your data is formatted as {["Vote", "User", "Poll"], ["Yes", "121", "1"], ...}

This function works by first figuring out the User and Poll sets

Once it knows how many total users (output List length) and total polls (output Array lengths), it can match pairs of them together and build the output

List<String[]> format(List<String[]> input)
{
    List<String[]> output = new ArrayList<String[]>();
    Set<String> users = new HashSet<String>();
    Set<String> pollSet = new HashSet<String>();
    Map<String, String> data = new HashMap<String, String>();

    for(String[] row : input) //figure out how many users and polls there are
    {
        users.add(row[1]);
        pollSet.add(row[2]);
        data.put(row[1] + "_" + row[2], row[0]); //link user_poll to Yes/No data
    }

    String[] polls = pollSet.toArray(new String[0]); //make the set be an array for easier access
    Arrays.sort(polls); //sort the polls here if you want to

    for(String user : users) //loop over users, since each row is 1 user
    {
        String[] row = new String[polls.length + 1]; //each row is poll1,poll2,...,pollN,user
        row[row.length - 1] = user;

        for(int i = 0; i < polls.length; i++)
            row[i] = data.get(user + "_" + polls[i]); //retrieve the Yes/No data for user_poll, no data fills in null
            //alternative if you want "NULL" instead of null
            //if((row[i] = data.get(user + "_" + polls[i]) == null)
                //row[i] = "NULL";

        output.add(row); //add completed row to the output
    }

    return output;
}

solved How to change data from long to wide form in Java