Set intersection: intersect

The intersect template function returns a list of items that appear in both of the two lists you provide. This is the set intersection operation: only items that exist in both lists are included in the result.

This is useful when you want to find what two collections have in common. For example, you might have a list of entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more] that are on and a list of entities in a specific room, and you want to know which entities in that room are currently on. Or you might want to find which devicesA device is a model representing a physical or logical unit that contains entities. appear in two different groups, or determine which family members are in both the “home” zone and the “allowed” list. Duplicates are removed from the result since it operates as a set operation.

Usage

Here’s how to use this template function. Copy any example and adjust it to your setup.

{{ intersect([1, 2, 3, 4], [3, 4, 5, 6]) }}

[3, 4]

{{ [1, 2, 3, 4] | intersect([3, 4, 5, 6]) }}

[3, 4]

Function signature

The signature is a technical summary of this template function. It shows the name of the function, the values (called parameters) it accepts, and what type of data each parameter expects (for example, a piece of text or a number).

Function parameters that have a = with a value after them are optional. If you leave them out, the default value shown is used automatically. Function parameters without a default are required.

intersect(
    value: list,
    other: list,
) -> list

Function parameters

The following parameters can be provided to this function.

Good to know

• Duplicates are removed in the result because this works as a set operation.
• Order is not preserved. Add | sort if you need a consistent order.
• Returns an empty list when the two lists share nothing.

Try it yourself

Ready to test this? Open Developer tools > Template, paste the example into the Template editor, and watch the result update on the right. Edit the values to see how the function adapts to your own entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this function comes up in automations and templates. Copy any example and adapt it to your setup.

Find entities that are in both groups

Determine which entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more] appear in two different groups.

{% set group_a = expand("group.downstairs_lights")
   | map(attribute="entity_id") | list %}
{% set group_b = expand("group.automated_lights")
   | map(attribute="entity_id") | list %}
{{ intersect(group_a, group_b) }}

["light.kitchen", "light.hallway"]

Find common items between two sensor lists

When two sensors each report a list of detected items, find which items are detected by both.

{% set cam1 = state_attr("sensor.camera_1", "detected_objects") %}
{% set cam2 = state_attr("sensor.camera_2", "detected_objects") %}
{{ intersect(cam1, cam2) }}

["person", "car"]

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with your template and expected result, or share on our subreddit /r/homeassistant.

Related template functions

These functions work well alongside this one:

• Set difference: difference - Returns items in the first list but not in the second (set difference).

• Set union: union - Returns all unique items from both lists (set union).

• Set symmetric difference: symmetric_difference - Returns items in either list but not in both.

• Convert to set: set - Converts an iterable to a set, removing duplicate values.