I have a CSV file that I import into my site using Feeds Tamper.
The CSV file has columns like
- URL path
 
- Favorite vegetable
 
- Favorite fruit
 
- Favorite pasta
 
In Drupal, my content type has a JSON Field, and I want to import "Favorite vegetable", "Favorite fruit", and "Favorite pasta" into the JSON field.
Is there a way to map all three favorites columns in the CSV file to the Drupal JSON field and combine their values in a Tamper plugin?  I can't find any way to pull in data from multiple sources (the three CSV columns) in a Tamper plugin.
Here's the structure of a Tamper plugin.
<?php
namespace Drupal\tamper\Plugin\Tamper;
use Drupal\tamper\Annotation\Tamper;
use Drupal\tamper\TamperableItemInterface;
use Drupal\tamper\TamperBase;
/**
 * Plugin implementation for CSV import. Copied from the encode plugin.
 *
 * @Tamper(
 *   id = "json_import",
 *   label = @Translation("JSON Import"),
 *   description = @Translation("Custom import for JSON."),
 *   category = "Text",
 *   handle_multiples = TRUE
 * )
 */
class JsonImport extends TamperBase {
  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    $config = parent::defaultConfiguration();
    return $config;
  }
  /**
   * {@inheritdoc}
   */
  public function tamper($data, TamperableItemInterface $item = NULL) {
    return $data;
  }
}