Computed Array Macros

groupBy.js

Ember.computed.groupBy = function(dependentKey, propertyKey) {
  return Ember.reduceComputed(dependentKey + ".@each." + propertyKey, {
    
    initialValue: Ember.MapWithDefault.create({
      defaultValue: function() {
        return Ember.Set.create();
      }
    }),

    addedItem: function(groups, item, changeMeta) {
      var groupValue = item.get(propertyKey),
          group = groups.get(groupValue);
  
      group.add(item);
      return groups;
    },
    
    removedItem: function(groups, item, changeMeta) {
      var groupValue = changeMeta.previousValues[propertyKey],
          group = groups.get(groupValue);
          
      group.remove(item);
      if (Ember.isEmpty(group)) {
        groups.remove(group);
      }
      return groups;
    }
    
  });
};

take.js

Ember.computed.take = function(dependentKey, limit) {
  return Ember.arrayComputed(dependentKey, {
    
    addedItem: function(array, item, changeMeta, instanceMeta) {
      if (changeMeta.index < limit) {
        array.insertAt(changeMeta.index, item);
      }
      if (array.get('length') > limit) {
        array.popObject();
      }
      return array;
    },
    
    removedItem: function(array, item, changeMeta, instanceMeta) {
      if (changeMeta.index < limit) {
        array.removeAt(changeMeta.index, 1);
      }
      if (changeMeta.arrayChanged.get('length') > limit) {
        array.insertAt(limit - 1, changeMeta.arrayChanged.objectAt(limit));
      }
      return array;
    }
    
  });
};