Adjust point sample process.

distribution/lib/Standard/Visualization/0.0.0-dev/src/Scatter_Plot.enso

@@ -158,40 +158,25 @@ type Extreme min_x max_x min_y max_y
 ## PRIVATE
 limit_data limit data = case limit of
     Nothing -> data
-    _ -> if (data.length <= limit) then data else
-        b = Vector.new_builder limit
-
+    _ -> if ((data.length <= limit) || (data.length == 0)) then data else
         x datum = (datum.get "x").unwrap
         y datum = (datum.get "y").unwrap
 
-        check_max_y min now = case min of
-            Extreme min_x max_x min_y Nothing -> Extreme min_x max_x min_y now
-            Extreme min_x max_x min_y max_y -> if y max_y < y now then @Tail_Call check_max_y (Extreme min_x max_x min_y now) max_y else
-                b.append now
-                min
-
-        check_min_y min now = case min of
-            Extreme min_x max_x Nothing max_y -> Extreme min_x max_x now max_y
-            Extreme min_x max_x min_y max_y -> if y min_y > y now then @Tail_Call check_min_y (Extreme min_x max_x now max_y) min_y else
-                check_max_y min now
-
-        check_max_x min now = case min of
-            Extreme min_x Nothing min_y max_y -> Extreme min_x now min_y max_y
-            Extreme min_x max_x min_y max_y -> if x max_x < x now then @Tail_Call check_max_x (Extreme min_x now min_y max_y) max_x else
-                check_min_y min now
-
-        check_min_x min now = case min of
-            Extreme Nothing max_x min_y max_y -> Extreme now max_x min_y max_y
-            Extreme min_x max_x min_y max_y -> if x min_x > x now then @Tail_Call check_min_x (Extreme now max_x min_y max_y) min_x else
-                check_max_x min now
+        update_extreme current idx point =
+            new_min_x = if x current.min_x.second > x point then [idx, point] else current.min_x
+            new_min_y = if y current.min_y.second > y point then [idx, point] else current.min_y
+            new_max_x = if x current.max_x.second < x point then [idx, point] else current.max_x
+            new_max_y = if y current.max_y.second < y point then [idx, point] else current.max_y
+            Extreme new_min_x new_max_x new_min_y new_max_y
 
-        extreme = case data.fold (Extreme Nothing Nothing Nothing Nothing) check_min_x of
-            Extreme min_x max_x min_y max_y -> [min_x, max_x, min_y, max_y].filter case _ of
-                Nothing -> False
-                _ -> True
+        first = [0, data.first]
+        bounds = case data.fold_with_index (Extreme first first first first) update_extreme of
+            Extreme min_x max_x min_y max_y ->  [min_x, max_x, min_y, max_y]
+            _ -> []
+        extreme = Map.from_vector bounds . values
 
         if limit <= extreme.length then extreme.take (First limit) else
-            extreme + b.to_vector.take (Sample limit-extreme.length)
+            extreme + data.take (Sample (limit - extreme.length))
 
 ## PRIVATE
 json_from_table : Table -> [Int]|Nothing -> Int|Nothing -> Json

test/Visualization_Tests/src/Scatter_Plot_Spec.enso

@@ -126,7 +126,7 @@ spec =
             json.fields.keys.should_equal ['axis','data']
             data = (json.fields.get 'data') . unwrap
             data.length . should_equal 10
-            (data.take (First 4)).to_text . should_equal "[[['x', 0], ['y', 225]], [['x', 29], ['y', 196]], [['x', 15], ['y', 0]], [['x', 1], ['y', 196]]]"
+            (data.take (First 3)).to_text . should_equal '[[[\'x\', 0], [\'y\', 225]], [[\'x\', 15], [\'y\', 0]], [[\'x\', 29], [\'y\', 196]]]'
 
         Test.specify "filter the elements" <|
             vector = [0,10,20,30]
@@ -141,3 +141,5 @@ spec =
         Test.specify "using indices for x if given a range" <|
             value = 2.up_to 5
             expect value no_labels '[{"x":0,"y":2},{"x":1,"y":3},{"x":2,"y":4}]'
+
+main = Test.Suite.run_main spec