array_flip.php

<?php
$flip_current = array_flip( $this->current_careers );
foreach ( $careers_feed as $career ) {
  
  /**
   * check if post with post_name = $career['id'] exists
   *
   * If so, skip and remove from delete
   */
  $exists       = $wpdb->get_var( $wpdb->prepare(
    "SELECT ID FROM $wpdb->posts WHERE post_status = 'publish' AND post_name = %s AND post_type='career'", $career['id'] ) );
  
  if ( is_null( $exists ) ) {
    $new_id = $this->create_career_post( $career );
    if ( $new_id ) {
      $careers_new[] = $new_id;
    }
  } else {
    /**
     * If career with same id in database then remove it from the "current_careers" array so it won't get deleted
     */
    unset( $this->current_careers[ $flip_current[ $exists ] ] );
  }

}