Question

I have the following function which compares the first column value in two 2D arrays.

var new_array = [['EMI_007','lion','cat'],
                 ['EMI_008','cat','dog']
                ];

var existing_array = [['EMI_002','cat','tiger'],
                     ['EMI_004','hen','pig'],
                     ['EMI_007','pigeon','hen'],
                     ['EMI_001','boar','tiger']
                ];

The value in new_array[i][0] is compared to the value in existing_array[j][0].

If they are the same, the entire row is replaced by the row in new_array, otherwise the new_array row is concatenated to the existing array.

In the above example, new_array is compared to existing_array.

EMI_007 exists in ‘existing_array’, so it’s replaced by ['EMI_007','lion','cat'] and [‘EMI_008′,’cat’,’dog’] is appended to the existing array.

I have created the following function but there seems to be an error.

If a row with an EMI id found in new_array does not exist in ‘existing_array’, it is inserted several times.

function concat_2D_array(existing_array, new_array){
    for (var i=0; i<new_array.length; i++) {
        for (var j=0; j<existing_array.length; j++) {
            if(new_array[i][0] == existing_array[j][0]){
            alert("ok,it already exists in the existing_array");
            existing_array.splice(j,1,new_array[i]);
            }
            else{
            alert("It is not in the existing array");
            // existing_array.concat(new_array[i]);
            }
        }
    }
    alert("returned existing_array"+existing_array)
    return existing_array;
}

Any help is most appreciated

Answer 1

The main issue with your code is that you are trying to add new item to existing array on each step and don’t leave the loop, once added.

function concat_2D_array(existing_array, new_array){
    for (var i=0; i<new_array.length; i++) {
        var j = 0;
        while(j<existing_array.length){
            if(new_array[i][0] == existing_array[j][0]){
                alert("ok,it already exists in the existing_array");
                existing_array.splice(j,1,new_array[i]);
                break;  // we found it, replaced it, leaving the loop
            } else if (j+1 >= existing_array.length){
                alert("It is not in the existing array");
                existing_array.splice(j+1,0,new_array[i]);
                break;  // we didn't find it, added it, leaving the loop
            } else {
                j++;
            }
        }
    }
    alert("returned existing_array"+existing_array)
    return existing_array;
}