add count

README.md

@@ -395,7 +395,7 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 [**util/sorted**(lt[, cmp, key, reverse])](https://openhome.cc/eGossip/OpenSCAD/lib3x-sorted.html) | sort a list.
 [**util/contains**(lt, elem)](https://openhome.cc/eGossip/OpenSCAD/lib3x-contains.html) | return `true` if `lt` contains `elem`.
 [**util/binary_search**(sorted, target[, lo, hi])](https://openhome.cc/eGossip/OpenSCAD/lib3x-binary_search.html) | search a value in a sorted list.
-
+[**util/count**(lt, test)](https://openhome.cc/eGossip/OpenSCAD/lib3x-count.html) | return the number of times `test` return `true` in the list.
 
 ## Maze
 

docs/lib3x-count.md

@@ -0,0 +1,15 @@
+# count
+
+Returns the number of times `test` return `true` in the list.
+
+**Since:** 3.3
+
+## Parameters
+
+- `lt` : The list.
+- `test` : A testing function.
+
+## Examples
+
+    points = [[7, 2, 2], [1, 1, 2], [3, 4, 2], [3, 4, 2], [1, 2, 3]];
+    assert(count(points, function(p) norm(p) > 5) == 3);

src/util/count.scad

@@ -1 +1,11 @@
+/**
+* count.scad
+*
+* @copyright Justin Lin, 2022
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib3x-count.html
+*
+**/ 
+
 function count(lt, test) = len([for(elem = lt) if(test(elem)) undef]);