public function indexBy($field)
    {
        $this->data = $this->executeIndexBy($this->data, $field);
        $this->indexBy = $field;
        return $this;
    }
public function indexBy($field)
    {
        $this->data = $this->executeIndexBy($this->data, $field);
        $this->indexBy = $field;
        return $this;
    }
public function indexBy ( $ field ) { $ this -> data = $ this -> executeIndexBy ( $ this -> data , $ field ) ; $ this -> indexBy = $ field ; return $ this ; }
Specifies a field to be the key of the fetched array

@param string $field
@return $this
Specifies a field to be the key of the fetched array