From 23dae20a546b51d0c87f95289f31966c48cafafa Mon Sep 17 00:00:00 2001
From: terminaldweller <thabogre@gmail.com>
Date: Fri, 8 Jul 2022 13:16:16 +0430
Subject: a simple decision tree implementation

---
 decision_tree/decision_tree.go | 106 +++++++++++++++++++++++++++++++++++++++++
 decision_tree/go.mod           |   3 ++
 2 files changed, 109 insertions(+)
 create mode 100644 decision_tree/decision_tree.go
 create mode 100644 decision_tree/go.mod

diff --git a/decision_tree/decision_tree.go b/decision_tree/decision_tree.go
new file mode 100644
index 0000000..2e80778
--- /dev/null
+++ b/decision_tree/decision_tree.go
@@ -0,0 +1,106 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"math/rand"
+	"time"
+)
+
+type Class int32
+
+const (
+	classOne Class = 0
+	classTwo       = 1
+)
+
+type pointType struct {
+	x     float32
+	y     float32
+	class Class
+}
+
+func generateRandData(n int32, points []pointType) {
+	rand.Seed(time.Now().UnixNano())
+	var i int32
+	for i = 0; i < n; i++ {
+		dirX := rand.Float32()
+		dirY := rand.Float32()
+		if dirX > 0.5 {
+
+			points[i].x = rand.Float32() * 20
+		} else {
+			points[i].x = -rand.Float32() * 20
+		}
+		if dirY > 0.5 {
+			points[i].y = rand.Float32() * 20
+		} else {
+			points[i].y = -rand.Float32() * 20
+		}
+		class := rand.Float32()
+		if class < 0.5 {
+			points[i].class = classOne
+		} else {
+			points[i].class = classTwo
+		}
+	}
+}
+
+func decisionTreeV1(points []pointType) {
+	for i := 0; i < len(points); i++ {
+		if points[i].x <= -12 {
+			if points[i].x <= 9 {
+				if points[i].y < 9 {
+
+				} else {
+
+				}
+			} else {
+
+			}
+		} else {
+
+		}
+	}
+}
+
+func calcClassProbs(points []pointType, classCount int) []float64 {
+	var counts = make([]int, classCount)
+	for i := 0; i < len(points); i++ {
+		counts[points[i].class]++
+	}
+
+	var probs = make([]float64, classCount)
+	for i := 0; i < classCount; i++ {
+		probs[i] = float64(counts[i]) / float64(len(points))
+	}
+
+	return probs
+}
+
+func calcEntropy(probs []float64) float64 {
+	var entropy float64
+
+	for i := 0; i < len(probs); i++ {
+		entropy += probs[i] * float64(math.Log2(probs[i]))
+	}
+
+	entropy = entropy * -1
+	return entropy
+}
+
+func main() {
+	var n int32 = 1000
+	var points = make([]pointType, n)
+	generateRandData(n, points)
+	var i int32
+	for i = 0; i < n; i++ {
+		fmt.Println(points[i].x, ":", points[i].y, ":", points[i].class)
+	}
+	probs := calcClassProbs(points, 2)
+	for i := 0; i < 2; i++ {
+		fmt.Println(probs[i])
+	}
+	entropy := calcEntropy(probs)
+	fmt.Println(entropy)
+}
diff --git a/decision_tree/go.mod b/decision_tree/go.mod
new file mode 100644
index 0000000..0ffdf1b
--- /dev/null
+++ b/decision_tree/go.mod
@@ -0,0 +1,3 @@
+module decision_tree
+
+go 1.18
-- 
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