How to merge two arrays in Java?

Question

Its not to concatenate but to merge two arrays so that they become array of name value pairs.

firstarray = ["a","aa","aaa"]
secondarray = ["b","bb","bbb"]
result = [["a","b"],["aa","bb"],["aaa","bbb"]]

What is the best way to do it?

Answer 1

in Java:

public static int [][] concat(int a[], int b[]) {
    int res[][] = new int[a.length][2];
    if (a.length != b.length) {
        throw new IllegalArgumentException("lenght are not equal, cannot perform");
    }
    for (int i = 0; i < a.length; i++) {
        res[i][0] = a[i];
        res[i][1] = b[i];
    }
    return res;
}

Answer 2

var result = [];

for(var i = 0; i<firstarray.length; i++) {
  result[i] = [firstarray[i], secondarray[i]];
}

Relies on the 2 arrays having a one-to-one relationship.

Answer 3

I would recommend you use the Java collection classes, and avoid using arrays. Only use arrays if/when you have to do so (for performance reasons, for example). Otherwise, stick with learning and becoming much more proficient with the Java Collections API.

If I were to approach this problem, assuming the first list had unique items (i.e. no duplicates), I would have two instances of List (as opposed to arrays). And then I would create an instance of Map into which I would place the contents of the two lists. LinkedHashMap is used to ensure the order of the items from the first list are preserved.

Here's the example code:

List<String> first = Arrays.asList(new String[] {"a", "aa", "aaa"});
List<String> second = Arrays.asList(new String[] {"b", "bb", "bbb"});
Map<String, String> keyValuePairs = new LinkedHashMap<String, String>();
for (int i = 0, count = first.size(); i < count; ++i) {
    keyValuePairs.put(first.get(i), second.get(i));
}

If one cannot assume the first list has unique values, then I would use List<List<String>>. Here's the example code:

List<String> first = Arrays.asList(new String[] {"a", "aa", "aaa"});
List<String> second = Arrays.asList(new String[] {"b", "bb", "bbb"});
List<List<String>> listOfList= new ArrayList<List<String>>();
for (int i = 0, count = first.size(); i < count; ++i) {
    List<String> list = new ArrayList();
    list.add(first.get(i));
    list.add(second.get(i));
    listOfList.add(list);
}

I don't think I can reinforce this point enough - avoid the use of arrays unless there is no way to do what you want with the Java collection classes. The only time I ever use arrays is to eke out performance at a verifiable bottleneck. And even then, I try to find a design level way around improving performance as opposed to using Java arrays.

Answer 4

public static int[] getmerge(int[] a, int[] b) {
    int[] c = new int[a.length + b.length];
    for (int i = 0; i < c.length; i++) {
        if (i < a.length) {
            c[i] = a[i];
        }
        if (i < b.length) {
            c[a.length + i] = b[i];
        }
    }
    return c;
}