Javascript: move objects from one array to another: Best approach?

Question

I have two arrays, called 'objects' and 'appliedObjects'. I'm trying to come up with an elegant way in Javascript and/or Angular to move objects from one array to another.

Initially I did something like this:

   $scope.remove = function () {
        angular.forEach($scope.appliedObjects, function (element, index) {
            if (element.selected) {
                element.selected = false;
                $scope.objects.push(element);
                $scope.appliedObjects.splice(index, 1);
            }
        });
    }

   $scope.add= function () {
        angular.forEach($scope.objects, function (element, index) {
            if (element.selected) {
                element.selected = false;
                $scope.appliedObjects.push(element);
                $scope.objects.splice(index, 1);
            }
        });
    }

But then I realized that when the value was removed from the looping array, and it would not add or remove every other item, since it went by index.

Then I tried using a temporary array to hold the list of items to be added or removed, and I started getting strange referential issues.

I'm starting to spin a bit on what the best solution to this problem would be...any help and/or guidance would much appreciated.

Answer 1

When a construct does too much automatically (like forEach, or even a for-loop, in this case), use a more primitive construct that allows you to say what should happen clearly, without need to work around the construct. Using a while loop, you can express what needs to happen without resorting to backing up or otherwise applying workarounds:

function moveSelected(src, dest)  {
    var i = 0;
    while ( i < src.length ) {
        var item = src[i];
        if (item.selected) {
            src.splice(i,1);
            dest.push(item);
        }
        else i++;
    }
}

Answer 2

function moveElements(source, target, moveCheck) {
    for (var i = 0; i < source.length; i++) {
        var element = source[i];
        if (moveCheck(element)) {
            source.splice(i, 1);
            target.push(element);
            i--;
        }
    } 
}

function selectionMoveCheck(element) {
   if (element.selected) {
       element.selected = false;
       return true;
   }
}

$scope.remove = function () {
    moveElements($scope.appliedObjects, $scope.objects, selectionMoveCheck);
}

$scope.add = function () {
    moveElements($scope.objects, $scope.appliedObjects, selectionMoveCheck);
}

Answer 3

You are altering the array while iterating on it, you will always miss some elements.

One way of doing it would be to use a third array to store the references of the objects that need to be removed from the array:

// "$scope.add" case
var objectsToRemove = [];

$scope.objects.forEach(function (value) {
  if (value.selected) {
    value.selected = false;
    $scope.appliedObjects.push(value);
    objectsToRemove.push(value);
  }
});

objectsToRemove.forEach(function (value) {
  $scope.objects.splice($scope.objects.indexOf(value), 1);
});

Answer 4

If you wish to move simply whole array you could do:

appliedObjects = objects;
objects = []

Of course it won't work if they were parameters of a function! Otherwise I cannot see other way than copying in the loop, e.g.

while (objects.length) {
    appliedObjects.push(objects[0]);
    objects.splice(0,1);
}

or if you like short code :) :

while (objects.length) appliedObjects.push(objects.splice(0,1));

check fiddle http://jsfiddle.net/060ywajm/