spatial/vptree: new package for vantage point tree NN search

spatial/vptree/vptree_simple_example_test.go

@@ -0,0 +1,60 @@
+// Copyright ©2019 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package vptree_test
+
+import (
+	"fmt"
+
+	"gonum.org/v1/gonum/spatial/vptree"
+)
+
+func ExampleTree() {
+	// Example data from https://en.wikipedia.org/wiki/K-d_tree
+	points := []vptree.Comparable{
+		vptree.Point{2, 3},
+		vptree.Point{5, 4},
+		vptree.Point{9, 6},
+		vptree.Point{4, 7},
+		vptree.Point{8, 1},
+		vptree.Point{7, 2},
+	}
+
+	t := vptree.New(points, 3, nil)
+	q := vptree.Point{8, 7}
+	p, d := t.Nearest(q)
+	fmt.Printf("%v is closest point to %v, d=%f\n", p, q, d)
+	// Output:
+	// [9 6] is closest point to [8 7], d=1.414214
+}
+
+func ExampleTree_Do() {
+	// Example data from https://en.wikipedia.org/wiki/K-d_tree
+	points := []vptree.Comparable{
+		vptree.Point{2, 3},
+		vptree.Point{5, 4},
+		vptree.Point{9, 6},
+		vptree.Point{4, 7},
+		vptree.Point{8, 1},
+		vptree.Point{7, 2},
+	}
+
+	// Print all points in the data set within 3 of (3, 5).
+	t := vptree.New(points, 0, nil)
+	q := vptree.Point{3, 5}
+	t.Do(func(c vptree.Comparable, _ int) (done bool) {
+		// Compare each distance and output points
+		// with a Euclidean distance less than or
+		// equal to 3. Distance returns the
+		// Euclidean distance between points.
+		if q.Distance(c) <= 3 {
+			fmt.Println(c)
+		}
+		return
+	})
+	// Unordered output:
+	// [2 3]
+	// [4 7]
+	// [5 4]
+}