Add reporter.Callback, sensible zero UpdateInterval

CHANGELOG.md

@@ -2,9 +2,14 @@
 
 ## [[unpublished]](https://github.com/mlange-42/arche-model/compare/v0.7.0...main)
 
+### Features
+
+* Adds `reporter.Callback` for direct retrieval of observer output in Go code (#61)
+
 ### Bugfixes
 
 * Fix typo in error message when adding UI system as normal system (#60)
+* Reporters did not work with unspecified UpdateInterval (#61)
 
 ## [[v0.7.0]](https://github.com/mlange-42/arche-model/compare/v0.6.0...v0.7.0)
 

reporter/callback.go

@@ -0,0 +1,40 @@
+package reporter
+
+import (
+	"github.com/mlange-42/arche-model/observer"
+	"github.com/mlange-42/arche/ecs"
+)
+
+// Callback reporter calling a function on each update.
+type Callback struct {
+	Observer       observer.Row // Observer to get data from.
+	UpdateInterval int          // Update/print interval in model ticks.
+	HeaderCallback func(header []string)
+	Callback       func(step int, row []float64)
+	step           int64
+}
+
+// Initialize the system
+func (s *Callback) Initialize(w *ecs.World) {
+	s.Observer.Initialize(w)
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
+	if s.HeaderCallback != nil {
+		s.HeaderCallback(s.Observer.Header())
+	}
+	s.step = 0
+}
+
+// Update the system
+func (s *Callback) Update(w *ecs.World) {
+	s.Observer.Update(w)
+	if s.step%int64(s.UpdateInterval) == 0 {
+		values := s.Observer.Values(w)
+		s.Callback(int(s.step), values)
+	}
+	s.step++
+}
+
+// Finalize the system
+func (s *Callback) Finalize(w *ecs.World) {}

reporter/callback_test.go

@@ -0,0 +1,34 @@
+package reporter_test
+
+import (
+	"fmt"
+
+	"github.com/mlange-42/arche-model/model"
+	"github.com/mlange-42/arche-model/reporter"
+	"github.com/mlange-42/arche-model/system"
+)
+
+func ExampleCallback() {
+	// Create a new model.
+	m := model.New()
+
+	data := [][]float64{}
+
+	// Add a Print reporter with an Observer.
+	m.AddSystem(&reporter.Callback{
+		Observer: &ExampleObserver{},
+		Callback: func(step int, row []float64) {
+			data = append(data, row)
+		},
+	})
+
+	// Add a termination system that ends the simulation.
+	m.AddSystem(&system.FixedTermination{Steps: 3})
+
+	// Run the simulation.
+	m.Run()
+
+	fmt.Println(data)
+	// Output:
+	// [[1 2 3] [1 2 3] [1 2 3]]
+}

reporter/csv.go

@@ -28,6 +28,9 @@ type CSV struct {
 func (s *CSV) Initialize(w *ecs.World) {
 	s.Observer.Initialize(w)
 	s.header = s.Observer.Header()
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
 	if s.Sep == "" {
 		s.Sep = ","
 	}

reporter/csv_snaphot.go

@@ -27,6 +27,9 @@ type SnapshotCSV struct {
 func (s *SnapshotCSV) Initialize(w *ecs.World) {
 	s.Observer.Initialize(w)
 	s.header = s.Observer.Header()
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
 
 	if s.Sep == "" {
 		s.Sep = ","

reporter/print.go

@@ -19,6 +19,9 @@ type Print struct {
 func (s *Print) Initialize(w *ecs.World) {
 	s.Observer.Initialize(w)
 	s.header = s.Observer.Header()
+	if s.UpdateInterval == 0 {
+		s.UpdateInterval = 1
+	}
 	s.step = 0
 }