Iterate over component data

Iterating over data is one of the most common tasks you need to perform when you create a system. A system typically processes a set of entities, reads data from one or more components, performs a calculation, and then writes the result to another component.

The most efficient way to iterate over entities and components is in a job that processes the components in order. This takes advantage of the processing power from all available cores and data locality to avoid CPU cache misses.

This section explains how to iterate over entity data in the following ways:

Topic	Description
Iterate over component data with SystemAPI.Query	Iterate through a collection of data on the main thread.
Iterate over component data with IJobEntity	Write once and create multiple schedules with IJobEntity.
Iterate over chunks of data with IJobChunk	Iterate over archetype chunks that contain matching entities with IJobChunk.
Iterate manually over data	Manually iterate over entities or archetype chunks.
Iterate over component data with Entities.ForEach	Use Entities.ForEach in SystemBase to iterate over entities.
Query data with an entity query	Find component data with entity queries.
Look up arbitrary data	Access arbitrary data without using an entity query.

Additional resources

You can also use the EntityQuery class to construct a view of your data that contains only the specific data you need for a given algorithm or process. Many of the iteration methods in the list above use an EntityQuery, either explicitly or internally. For more information, see Querying entity data with an entity query.