Merge pull request #20 from nhartland/edit_distance

Edit Distance method

CHANGELOG.md

@@ -73,13 +73,14 @@ Initial release
 # 0.5 (WIP)
 
 ## Features
-- Convex hull computation
+ - Convex hull computation
+ - Edit distance between patterns
 
 ## Bugfix
  - Including the circle raster unit test.
+ - Require a radius of at least 1 for primitives.circle
 
 ## Misc
- - Require a radius of at least 1 for primitives.circle
  - Ordering the example neighbourhood vector lists clockwise
  - Improved error messages on some subpattern methods
  - Slightly improved example gallery generation

forma/pattern.lua

@@ -234,6 +234,17 @@ function pattern.size_sort(pa, pb)
     return pa:size() > pb:size()
 end
 
+--- Return the total number of differing cells between two patterns.
+-- @param a first pattern for edit distance calculation
+-- @param b second pattern for edit distance calculation
+function pattern.edit_distance(a, b)
+    assert(getmetatable(a) == pattern, "pattern.edit_distance requires a pattern as the first argument")
+    assert(getmetatable(b) == pattern, "pattern.edit_distance requires a pattern as the second argument")
+    local common = pattern.intersection(a,b)
+    local edit_distance = (a - common):size() + (b-common):size()
+    return edit_distance
+end
+
 -----------------------
 --- Iterators.
 -- @section Iterators

tests/pattern.lua

@@ -340,3 +340,19 @@ function testPattern:testPacktileCentre()
     lu.assertEquals(pp.x, 1)
     lu.assertEquals(pp.y, 1)
 end
+
+function testPattern:testEditDistance()
+    -- Self-distances
+    lu.assertEquals(self.pattern_1:edit_distance(self.pattern_1), 0)
+    lu.assertEquals(self.pattern_2:edit_distance(self.pattern_2), 0)
+    lu.assertEquals(self.pattern_3:edit_distance(self.pattern_3), 0)
+    -- Non-overlapping
+    local p1 = pattern.new({{1,0},
+                            {0,1}})
+    local p2 = pattern.new({{0,1},
+                            {1,0}})
+    lu.assertEquals(p1:edit_distance(p2), 4)
+    -- Overlapping
+    local edit_distance_23 = self.pattern_2:edit_distance(self.pattern_3)
+    lu.assertEquals(edit_distance_23, 5*5 - 1) -- one common point
+end