(Java) Populate a 2d array with contents from another 2d array AND a map

Question

I have this map:

static Map<String, String> myMap = new HashMap<>();

static {
    myMap.put("param1","param11");
    myMap.put("param2","param22");
}

and I have this 2d array:

Object[][] objArr1 = new Object[][]{
             {"1", 1},
             {"2", 2}
    };

I want to "merge" the above into another 2d array:

Object[][] objArr3 = new Object[][];

So the resulting content of objArr3 is (in no particular order):

 {"1", 1, "param1","param11"},
 {"1", 1, "param2","param22"},

 {"2", 2,"param1","param11"},
 {"2", 2,"param2","param22"

I understand that I probably need

new Object[objArr1 * myMap.size()][4];

but can't create a proper nested for loop to do this. I've tried to combine solutions from here and here but to no avail. Any help greatly appreciated.

We need to see these attempts to be able to help you. Please read the link I offered thoroughly to understand what you should do now. — Joe C, Oct 03 '17 at 16:06

Joris Schellekens · Accepted Answer · 2017-10-05T12:59:42.350

This should work.
It iterates over all rows of the array, and all key/value pairs of the map, combining both of them in a new row. And then putting each row in the output-array.

static Map<String, String> map1 = new HashMap<>();

static {
    map1.put("param1","param11");
    map1.put("param2","param22");
}

static Object[][] array1 = new Object[][]{
            {"1", 1},
            {"2", 2}
};

public static void main (String[] args) throws java.lang.Exception
{
    // the new array has precisely N*M rows
    // where N is the number of rows in the input array
    // and M is the number of entries in the map
    Object[][] newArray = new Object[array1.length * map1.size()][4];
    int index = 0;
    for(int row=0;row<array1.length;row++)
    {
        for(Map.Entry<String, String> en : map1.entrySet())
        {
            Object[] newRow = new Object[4];
            newRow[0] = array1[row][0];
            newRow[1] = array1[row][1];
            newRow[2] = en.getKey();
            newRow[3] = en.getValue();
            newArray[index] = newRow;
            index++;
        }
    }
}

if I then output the array, I get

1 1 param1 param11
1 1 param2 param22
2 2 param1 param11
2 2 param2 param22

thanks. newArray[index] = newRow; was the key part i was missing — Andrejs, Oct 03 '17 at 16:51
Actually, this doesn't produce exactly the expected content of objArr3 mentioned in question. — Andrejs, Oct 05 '17 at 11:19
I forgot to index array1 on row. I've changed the code. It's only a slight modification. And I added my output. — Joris Schellekens, Oct 05 '17 at 13:00

score 0 · Answer 2 · answered Oct 05 '17 at 11:28

I needed an Object[][] as a final product for TestNg's @DataPovider, but I couldn't get around problems due to arrays being of fixed size. So I do all the manipulations with a list of lists and as a final step convert that to a 2d array:

public class main {

static Map<Object, Object> myMap = new HashMap<>();

static {
     myMap.put("1","1");
     myMap.put("2","2");
     myMap.put("3","3");
}


public static void main(String[] args){

    List<List<Object>> list = asList(
                         asList("param1", "param11"),
                         asList("param2", "param22")
                       );

    Object[][] finaList = mergeListWithMap(list, myMap);

    System.out.println(Arrays.deepToString(finaList));

}

private static Object[][] mergeListWithMap(List<List<Object>> list, Map<Object, Object> myMap) {
    List<List<Object>> newList = new ArrayList<>();

    for(List<Object> o : list){

         for(Map.Entry<Object, Object> en : myMap.entrySet()){
                List<Object> nl = new ArrayList<>(o); // copy original containing "param<x>", "param<xx>"
                nl.add(en.getKey());       // append               
                nl.add(en.getValue());     // append
                newList.add(nl);           // add final result to new list to be returned
         }
    }

    // Convert list of lists -> 2d-array
    Object[][] finaList = newList.stream()
            .map(l -> l.stream().toArray(Object[]::new))
            .toArray(Object[][]::new);

    return finaList;
}


private static <T> List<T> asList(T ... items) {
    List<T> list = new ArrayList<>();
    for (T item : items) {
        list.add(item);
    }
    return list;
}

}

Output:

 [param1, param11, 1, 1]
 [param1, param11, 2, 2]
 [param1, param11, 3, 3]
 [param2, param22, 1, 1]
 [param2, param22, 2, 2]
 [param2, param22, 3, 3]

(Java) Populate a 2d array with contents from another 2d array AND a map

2 Answers2