Filtering entries by multiple URL parameters on the front end

Question

This answer here helped me get multiple same-name parameters to filter entries: (ex: ?recipe=healthy&recipe=salad&recipe=dinner)

Now I'm looking for a way to get multiple different parameters to help sort entries on the front-end. Something like:
?collection=healthy&ingredient=salad&meal=dinner

The code I have now is this (pretty much verbatim what came from the answer linked above):

{# Get search parameters from the URL query string #}
{% set collectionQuery = craft.request.getParam('collection') %}

{# Start an array of search parameters (relationParam) with 'and' to match ALL categories #}
{% set relationParam = ['and'] %}

{# Find categories that match the slugs in your query string... #}
{% for querySlug in collectionQuery %}
  {% set collectionCategory = craft.categories.group('recipes').slug(querySlug) %}

  {# And merge them into the relationParam array. #}
  {% set relationParam = relationParam|merge({targetElement: collectionCategory}) %}
{% endfor %}

{# Avoid passing an array with `['and']` only #}
{% if relationParam|length < 2 %}
  {% set relationParam = '' %}
{% endif %}

{% set searchParams = {
  relatedTo:  relationParam,
  section: 'generalContent',
  type: 'recipes'
} %}

<form action="/recipes">
  {% for category in craft.categories.group('recipes').level('1') %}
    <div style="display: inline-block;">
    <select name="{{ category.slug }}[]" onchange="this.form.submit()">
      <option name="{{ category.slug }}[]" value="">Any {{ category.title }}</option>

      {% for categoryChild in category.children() %}
        <option name="{{ category.slug }}[]" value="{{ categoryChild.slug }}"{{ categoryChild.slug in collectionQuery  ? 'selected'}}>{{ categoryChild.title }}</option>
      {% endfor %}
    </select>
    </div>
  {% endfor %}
</form>

{% paginate craft.entries(searchParams) as entries %}
    ...
{% endpaginate %}

Answer 1

You need to get each parameter from the URL separately and repeat the steps you already did for "collection":

• Get search parameters from the URL query string
• Find categories that match the slugs in your query string
• And merge them into the relationParam array.