From c37374c369ddc55179f54eebb99d64c6844a9cc0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Rivi=C3=A8re?= <fil@rezo.net>
Date: Fri, 5 Jun 2020 15:57:15 +0200
Subject: [PATCH] quadtree.find(x, y, radius, *filter*)

closes https://github.com/d3/d3-quadtree/issues/19
---
 README.md         |  4 ++--
 src/find.js       | 16 +++++++++++-----
 test/find-test.js |  9 +++++++++
 3 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index 05692ff..a76923f 100644
--- a/README.md
+++ b/README.md
@@ -121,10 +121,10 @@ Returns an array of all data in the quadtree.
 
 Returns the total number of data in the quadtree.
 
-<a name="quadtree_find" href="#quadtree_find">#</a> <i>quadtree</i>.<b>find</b>(<i>x</i>, <i>y</i>[, <i>radius</i>])
+<a name="quadtree_find" href="#quadtree_find">#</a> <i>quadtree</i>.<b>find</b>(<i>x</i>, <i>y</i>[, <i>radius</i>][, <i>filter</i>])
  [<>](https://github.com/d3/d3-quadtree/blob/master/src/find.js "Source")
 
-Returns the datum closest to the position ⟨*x*,*y*⟩ with the given search *radius*. If *radius* is not specified, it defaults to infinity. If there is no datum within the search area, returns undefined.
+Returns the datum closest to the position ⟨*x*,*y*⟩ with the given search *radius* that satisfies the *filter*. If *radius* is not specified, it defaults to infinity. If *filter* is not specified, all data are considered. If there is no acceptable datum within the search area, returns undefined.
 
 <a name="quadtree_visit" href="#quadtree_visit">#</a> <i>quadtree</i>.<b>visit</b>(<i>callback</i>)
  [<>](https://github.com/d3/d3-quadtree/blob/master/src/visit.js "Source")
diff --git a/src/find.js b/src/find.js
index e9db6c4..94c412e 100644
--- a/src/find.js
+++ b/src/find.js
@@ -1,6 +1,6 @@
 import Quad from "./quad.js";
 
-export default function(x, y, radius) {
+export default function(x, y, radius, filter) {
   var data,
       x0 = this._x0,
       y0 = this._y0,
@@ -58,10 +58,16 @@ export default function(x, y, radius) {
           dy = y - +this._y.call(null, node.data),
           d2 = dx * dx + dy * dy;
       if (d2 < radius) {
-        var d = Math.sqrt(radius = d2);
-        x0 = x - d, y0 = y - d;
-        x3 = x + d, y3 = y + d;
-        data = node.data;
+        var f, d;
+        do {
+          if (!filter || filter(node.data)) f = node;
+        } while (!f && (node = node.next));
+        if (f) {
+          d = Math.sqrt(radius = d2);
+          x0 = x - d, y0 = y - d;
+          x3 = x + d, y3 = y + d;
+          data = f.data;
+        }
       }
     }
   }
diff --git a/test/find-test.js b/test/find-test.js
index 82fc217..977a79f 100644
--- a/test/find-test.js
+++ b/test/find-test.js
@@ -32,3 +32,12 @@ tape("quadtree.find(x, y, null) treats the given radius as Infinity", function(t
   test.deepEqual(q.find(20, 20, undefined), [0, 0]);
   test.end();
 });
+
+tape("quadtree.find(x, y, radius, filter) considers only filtered points", function(test) {
+  var q = d3_quadtree.quadtree([[0, 0, "red"], [100, 0, "blue"], [100, 0, "blue"], [0, 100, "red"], [100, 100, "red"], [100, 100, "blue"]]);
+  test.deepEqual(q.find(20, 0, null, d => d[2] == "red"), [0, 0, "red"]);
+  test.deepEqual(q.find(20, 0, null, d => d[2] == "blue"), [100, 0, "blue"]);
+  test.deepEqual(q.find(20, 0, 50, d => d[2] == "blue"), undefined);
+  test.deepEqual(q.find(20, 0, null, d => d[2] == "green"), undefined);
+  test.end();
+});