gistfile1.php

<?php
class DoctrineItemSummaryListener implements EventSubscriber
{
    /** @var TagcloudGenerator */
    private $tagcloud;

    public function __construct(TagcloudGenerator $tagcloud)
    {
        $this->tagcloud = $tagcloud;
    }

    public function getSubscribedEvents() {
        return ['prePersist', 'preUpdate'];
    }

    public function prePersist(LifecycleEventArgs $event)
    {
        $entity = $event->getEntity();

        if (!$entity instanceof Item) {
            return;
        }

        $entity->setSummary($entity->computeSummary());
    }

    public function preUpdate(PreUpdateEventArgs $event)
    {
        $entity = $event->getEntity();

        if (!$entity instanceof Item) {
            return;
        }

        $summary = $entity->computeSummary();

        // special treatment for Text type
        if ($entity instanceof Text) {
            $summary = [];
            $answers = $entity->getAnswers()->map(function (ItemAnswer $answer) { return $answer->getValue(); })->getValues();

            foreach (json_decode($this->tagcloud->getTagcloudFromArray('survey.item', $entity->getId(), $answers, true)) ?: [] as $tuple) {
                $summary[$tuple[0]] = $tuple[1];
            }
        }

        // now alter the current options value
        $options = $entity->getOptions();
        $options['cached'] = ['summary' => $summary];

        $event->setNewValue('options', $options);
    }
}