Sort and filter data in GridView Yii2 where column is not in database

STEP 1: Add a getter function to your base Risks model:

public function getPriority() {
    return ($this->probability * $this->influence);
}

STEP 2: Add an attribute priority to your model RisksSearch and configure your rules.

/* your calculated attribute */
public $priority;

/* setup rules */
public function rules() {
   return [
       /* your other rules */
       [['priority'], 'safe']
   ];
}

STEP 3: Edit the search() method to include the calculated field priority

public function search($params) {

    $query = Person::find();

    $query->select('*, (probability * influence) as priority');

    $dataProvider = new ActiveDataProvider([
        'query' => $query,
    ]);

    /**
     * Setup your sorting attributes
     * Note: This is setup before $this->load($params)
     */
    $dataProvider->setSort([
        'attributes' => [
            'id',
            'priority' => [
                'asc' => ['priority' => SORT_ASC],
                'desc' => ['priority' => SORT_DESC],
                'label' => 'Priority',
                'default' => SORT_ASC
            ],
        ]
    ]);
    ...

STEP 4: Add $query->andFilterWhere() after $this->load($params) to be able to filter the calculated field

// use the operator you wish, i.e. '=', '>', '<' etc
$query->andFilterWhere(['=', '(probability * influence)', $this->priority]);

Removed

      $query->select('*, (probability * influence) as priority');

changed

          'priority' => [
                'asc' => ['(probability * influence)' => SORT_ASC],
                'desc' => ['(probability * influence)' => SORT_DESC],
                'label' => 'Priority',
              ],

and after $this->load($params);

          $query->andFilterWhere(['=', '(probability * influence)', $this->priority]);

And search works as needed! :)

Thanks for help!