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    Filtering data

    You can filter the data in an Entities.ForEach expression, either by change, or by shared component.

    Change filtering

    You can use WithChangeFilter<T> to enable change filtering, which processes components only if another component in the entity has changed since the last time the current SystemBase instance has run. The component type in the change filter must either be in the lambda expression parameter list, or part of a WithAll<T> statement. For example:

    
    Entities
        .WithChangeFilter<Source>()
        .ForEach((ref Destination outputData,
            in Source inputData) =>
            {
                /* Do work */
            })
        .ScheduleParallel();
    

    An entity query supports change filtering on up to two component types.

    Unity applies change filtering at the archetype chunk level. If any code accesses a component in a chunk that has write access, then Unity marks that component type in that archetype chunk as changed, even if the code didn’t change any data.

    Shared component filtering

    Unity groups entities with shared components into chunks with other entities that have the same value for their shared components. To select groups of entities that have specific shared component values, use the WithSharedComponentFilter method.

    The following example selects entities grouped by a Cohort ISharedComponentData. The lambda expression in this example sets a DisplayColor IComponentData component based on the entity’s cohort:

    
    [RequireMatchingQueriesForUpdate]
    public partial class ColorCycleJob : SystemBase
    {
        protected unsafe override void OnUpdate()
        {
    
            EntityManager.GetAllUniqueSharedComponents<Cohort>(out var cohorts, Allocator.Temp);
            for (int i=0; i<cohorts.Length; i++)
            {
                var cohort = cohorts[i];
                DisplayColor newColor = ColorTable.GetNextColor(cohort.Value);
                Entities.WithSharedComponentFilter(cohort)
                    .ForEach((ref DisplayColor color) => { color = newColor; })
                    .ScheduleParallel();
            }
        }
    }
    

    The example uses the EntityManager to get all the unique cohort values. It then schedules a lambda job for each cohort, and passes the new color to the lambda expression as a captured variable.

    In This Article
    • Change filtering
    • Shared component filtering
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