list_diff 1.2.0

📃 Calculates a minimal list of operations that convert one list into another if applied in order.

Offers a diff method that accepts two Lists and returns a list of Operations for turning the first list into the second one:

var operations = await diff(
  ['coconut', 'nut', 'peanut'],
  ['kiwi', 'coconut', 'maracuja', 'nut', 'banana'],
);
operations.forEach(print);

// Operations:
// Insertion of kiwi at 0.
// Insertion of maracuja at 2.
// Insertion of banana at 4.
// Deletion of peanut at 5.

Operations are either an insertion or deletion of an item at an index. You can also directly apply them to a list:

// Let's try it out!
var fruitBowl = ['coconut', 'nut', 'peanut'];

for (var operation in operations) {
    operation.applyTo(fruitBowl);
}

// Transforming:
// [coconut, nut, peanut]
// [kiwi, coconut, nut, peanut]
// [kiwi, coconut, maracuja, nut, peanut]
// [kiwi, coconut, maracuja, nut, banana, peanut]
// [kiwi, coconut, maracuja, nut, banana]

The lists' items are compared using their == operator.

A word about performance and threading

The current version of the function is not as performant as it could be. The runtime is currently O(N*M), where N and M are the lengths of the lists.

If the data sets are large, the diff function automatically spawns an isolate. If you don't want more control on whether an isolate should be spawned, you can also explicitly set the [spawnIsolate] parameter:

var operations = await diff(first, second, spawnIsolate: true);

For Flutter users

[diff] can be used to calculate updates for an [AnimatedList]:

final _listKey = GlobalKey<AnimatedListState>();
List<String> _lastFruits;
...
StreamBuilder<String>(
  stream: fruitStream,
  initialData: [],
  builder: (context, snapshot) {
    for (var operation in await diff(_lastFruits, snapshot.data)) {
      if (operation.isInsertion) {
        _listKey.insertItem(operation.index);
      } else {
        _listKey.removeItem(operation.index, (context, animation) => ...);
      }
    }
    return AnimatedList(
      key: _listKey,
      itemBuilder: (context, index, animation) => ...,
    );
  },
),