contains_set

Checks if an array contains a value using optimized Set-based lookup. For large arrays (100+ items), this is significantly faster than the native contains operator, which uses O(n) linear search.

{% assign all_skus = products | map: "sku" %}

{% if all_skus | contains_set: "ABC123" %}
  SKU exists in catalog
{% endif %}

Syntax

{{ array | contains_set: value }}

Parameter	Description
array	Array to search in
value	Value to search for

Performance

Array Size	Native contains	contains_set
100 items	O(100) per check	O(1) per check
10,000 items	O(10,000) per check	O(1) per check
250,000 items	O(250,000) per check	O(1) per check

The filter automatically caches the Set representation, so subsequent lookups on the same array are instant.

Examples

Check if SKU exists in large inventory:

{% comment %} Fetch all existing SKUs from Shopify {% endcomment %}
{% assign all_skus = "[]" | parse %}
{% for n in (0..100) %}
  {% graphql query: sku_query, variables: vars as result %}
  {% for edge in result.productVariants.edges %}
    {% assign all_skus = all_skus | push: edge.node.sku %}
  {% endfor %}
  {% unless result.productVariants.pageInfo.hasNextPage %}{% break %}{% endunless %}
{% endfor %}

{% comment %} Check each import row against existing SKUs {% endcomment %}
{% for row in import_data %}
  {% if all_skus | contains_set: row.sku %}
    {% log "SKU already exists: " | append: row.sku %}
  {% else %}
    {% comment %} Create new product {% endcomment %}
  {% endif %}
{% endfor %}

Filter items not in exclusion list:

{% assign excluded_tags = "sale,clearance,discontinued" | split: "," %}
{% assign products_to_process = "[]" | parse %}

{% for product in all_products %}
  {% assign dominated_value = false %}
  {% for tag in product.tags %}
    {% if excluded_tags | contains_set: tag %}
      {% assign dominated_value = true %}
      {% break %}
    {% endif %}
  {% endfor %}
  {% unless dominated_value %}
    {% assign products_to_process = products_to_process | push: product %}
  {% endunless %}
{% endfor %}

Validate order items against allowed products:

{% assign allowed_product_ids = allowed_products | map: "id" %}

{% for line_item in order.line_items %}
  {% unless allowed_product_ids | contains_set: line_item.product_id %}
    {% log "Unauthorized product in order: " | append: line_item.title %}
    {% assign has_unauthorized = true %}
  {% endunless %}
{% endfor %}

When to Use

Scenario	Recommended
Single lookup	Use native contains
Multiple lookups on same array	Use contains_set
Array with 100+ items	Use contains_set
Small arrays (<100 items)	Either works, contains_set has slight overhead

Notes

• Works with strings too: "hello world" | contains_set: "world" returns true

• Returns false for null or undefined input arrays