concat

Concatenates two arrays together or appends elements to an array. Returns a new array without modifying the original arrays.

{% assign fruits = "apple,banana" | split: "," %}
{% assign more_fruits = "cherry,date" | split: "," %}

{% assign all_fruits = fruits | concat: more_fruits %}
{% log all_fruits | join: ", " %}

Output:

apple, banana, cherry, date

Syntax

{{ array | concat: other_array }}
{{ array | concat: element }}

Parameter	Description
array	The base array
other_array	Array to append, or single element to add

Examples

Combine two arrays:

{% assign domestic_orders = orders | where: "shipping_country", "US" %}
{% assign international_orders = orders | where: "shipping_country", "CA" %}

{% assign north_america_orders = domestic_orders | concat: international_orders %}

{% log "Total North America orders: " | append: north_america_orders.size %}

Build array from multiple sources:

{% assign all_products = "[]" | parse %}

{% for collection in collections %}
  {% assign collection_products = collection.products %}
  {% assign all_products = all_products | concat: collection_products %}
{% endfor %}

{% log "Total products across all collections: " | append: all_products.size %}

Merge GraphQL pagination results:

{% assign all_variants = "[]" | parse %}
{% assign cursor = "null" | parse %}

{% for n in (0..100) %}
  {% graphql query: variants_query, variables: vars as result %}

  {% assign page_variants = result.productVariants.edges | map: "node" %}
  {% assign all_variants = all_variants | concat: page_variants %}

  {% unless result.productVariants.pageInfo.hasNextPage %}
    {% break %}
  {% endunless %}

  {% assign cursor = result.productVariants.edges.last.cursor %}
{% endfor %}

{% log "Fetched " | append: all_variants.size | append: " variants" %}

Combine tags from multiple products:

{% assign all_tags = "[]" | parse %}

{% for product in products %}
  {% assign product_tags = product.tags | split: ", " %}
  {% assign all_tags = all_tags | concat: product_tags %}
{% endfor %}

{% assign unique_tags = all_tags | uniq | sort %}
{% log "Unique tags: " | append: unique_tags | join: ", " %}

Add single element to array:

{% assign items = "[]" | parse %}

{% if condition_a %}
  {% assign items = items | concat: "item_a" %}
{% endif %}

{% if condition_b %}
  {% assign items = items | concat: "item_b" %}
{% endif %}

{% log items %}

Merge line items from multiple orders:

{% assign all_line_items = "[]" | parse %}

{% for order in orders %}
  {% assign all_line_items = all_line_items | concat: order.line_items %}
{% endfor %}

{% log "Total line items: " | append: all_line_items.size %}

Combine API responses:

{% assign all_results = "[]" | parse %}

{% for endpoint in endpoints %}
  {% http url: endpoint as response %}
  {% if response.ok and response.body.items %}
    {% assign all_results = all_results | concat: response.body.items %}
  {% endif %}
{% endfor %}

Build notification recipients:

{% assign recipients = "[]" | parse %}

{% comment %} Add order customer {% endcomment %}
{% assign recipients = recipients | concat: order.customer.email %}

{% comment %} Add store admins {% endcomment %}
{% assign admin_emails = "[e-mail],[e-mail]" | split: "," %}
{% assign recipients = recipients | concat: admin_emails %}

{% comment %} Add vendor if applicable {% endcomment %}
{% if order.vendor_email %}
  {% assign recipients = recipients | concat: order.vendor_email %}
{% endif %}

{% assign unique_recipients = recipients | uniq %}
{% log "Sending to: " | append: unique_recipients | join: ", " %}

Comparison: concat vs push

Feature	concat	push
Modifies original	No (returns new array)	Yes (mutates in place)
Can add arrays	Yes (flattens one level)	No (adds array as single element)
Use case	Merging arrays	Adding single items

Example difference:

{% assign arr = "[1, 2]" | parse %}
{% assign to_add = "[3, 4]" | parse %}

{% comment %} concat - merges arrays {% endcomment %}
{% assign result_concat = arr | concat: to_add %}
{{ result_concat | json }}
{% comment %} Output: [1, 2, 3, 4] {% endcomment %}

{% comment %} push - adds as single element {% endcomment %}
{% push arr, to_add %}
{{ arr | json }}
{% comment %} Output: [1, 2, [3, 4]] {% endcomment %}

Performance Tip

When building large arrays in a loop, concat creates a new array each time. For better performance with many iterations, consider using push which modifies in place:

{% comment %} Less efficient (many array copies) {% endcomment %}
{% assign result = "[]" | parse %}
{% for item in large_array %}
  {% assign result = result | concat: item %}
{% endfor %}

{% comment %} More efficient (in-place modification) {% endcomment %}
{% assign result = "[]" | parse %}
{% for item in large_array %}
  {% push result, item %}
{% endfor %}

Notes

• Returns a new array; original arrays are not modified

• When concatenating arrays, elements are flattened one level deep

• When concatenating a single value, it's added as-is

• Works with any array types (strings, numbers, objects)

• For adding single items in a loop, prefer push for better performance

• See also: push for in-place array modification