Lazy scatterplot for Vector & Table (#3655)

First of all this PR demonstrates how to implement _lazy visualization_:
- one needs to write/enhance Enso visualization libraries - this PR adds two optional parameters (`bounds` and `limit`) to `process_to_json_text` function.
- the `process_to_json_text` can be tested by standard Enso test harness which this PR also does
- then one has to modify JavaScript on the IDE side to construct `setPreprocessor` expression using the optional parameters

The idea of _scatter plot lazy visualization_ is to limit the amount of points the IDE requests. Initially the limit is set to `limit=1024`. The `Scatter_Plot.enso` then processes the data and selects/generates the `limit` subset. Right now it includes `min`, `max` in both `x`, `y` axis plus randomly chosen points up to the `limit`.

![Zooming In](https://user-images.githubusercontent.com/26887752/185336126-f4fbd914-7fd8-4f0b-8377-178095401f46.png)

The D3 visualization widget is capable of _zooming in_. When that happens the JavaScript widget composes new expression with `bounds` set to the newly visible area. By calling `setPreprocessor` the engine recomputes the visualization data, filters out any data outside of the `bounds` and selects another `limit` points from the new data. The IDE visualization then updates itself to display these more detailed data. Users can zoom-in to see the smallest detail where the number of points gets bellow `limit` or they can select _Fit all_ to see all the data without any `bounds`.

# Important Notes
Randomly selecting `limit` samples from the dataset may be misleading. Probably implementing _k-means clustering_ (where `k=limit`) would generate more representative approximation.

CHANGELOG.md

@@ -42,6 +42,7 @@
   visualizations. (Previously, they were placed to the left of the
   visualizations.)
 - [Fixed histograms coloring and added a color legend.][3153]
+- [Lazy visualization for scatter plot.][3655]
 - [Fixed broken node whose expression contains non-ASCII characters.][3166]
 - [Fixed developer console warnings about views being created but not
   registered.][3181]
@@ -185,6 +186,7 @@
 [debug-shortcuts]:
   https://github.com/enso-org/enso/blob/develop/app/gui/docs/product/shortcuts.md#debug
 [3153]: https://github.com/enso-org/enso/pull/3153
+[3655]: https://github.com/enso-org/enso/pull/3655
 [3166]: https://github.com/enso-org/enso/pull/3166
 [3181]: https://github.com/enso-org/enso/pull/3181
 [3186]: https://github.com/enso-org/enso/pull/3186

app/gui/view/graph-editor/src/builtin/visualization/java_script/scatterPlot.js

@@ -17,6 +17,7 @@ const LINEAR_SCALE = 'linear'
 const LOGARITHMIC_SCALE = 'logarithmic'
 const VISIBLE_POINTS = 'visible'
 const BUTTONS_HEIGHT = 25
+const DEFAULT_LIMIT = 1024
 
 /**
  * A d3.js ScatterPlot visualization.
@@ -49,7 +50,9 @@ class ScatterPlot extends Visualization {
 
     constructor(data) {
         super(data)
-        this.setPreprocessor('process_to_json_text', 'Standard.Visualization.Scatter_Plot')
+        this.bounds = null
+        this.limit = DEFAULT_LIMIT
+        this.updatePreprocessor()
         this.dataPoints = []
         this.axis = {
             x: { scale: LINEAR_SCALE },
@@ -58,6 +61,14 @@ class ScatterPlot extends Visualization {
         this.points = { labels: VISIBLE_POINTS }
     }
 
+    updatePreprocessor() {
+        let fn = 'x -> process_to_json_text x limit=' + this.limit
+        if (this.bounds) {
+            fn += ' bounds=[' + this.bounds.join(',') + ']'
+        }
+        this.setPreprocessor(fn, 'Standard.Visualization.Scatter_Plot')
+    }
+
     /**
      * Presents a scatterplot visualization after receiving `data`.
      */
@@ -377,6 +388,9 @@ class ScatterPlot extends Visualization {
             let yMin = zoom.transformedScale.yScale.invert(extent[1][1])
             let yMax = zoom.transformedScale.yScale.invert(extent[0][1])
 
+            this.bounds = [xMin, yMin, xMax, yMax]
+            this.updatePreprocessor()
+
             zoom.transformedScale.xScale.domain([xMin, xMax])
             zoom.transformedScale.yScale.domain([yMin, yMax])
 
@@ -726,7 +740,7 @@ class ScatterPlot extends Visualization {
         addStyleToElem(
             'button',
             `
-            margin-left: 5px; 
+            margin-left: 5px;
             margin-bottom: 5px;
             display: inline-block;
             padding: 2px 10px;
@@ -806,6 +820,10 @@ class ScatterPlot extends Visualization {
             zoom.transformedScale.yScale.domain(domainY)
 
             self.zoomingHelper(zoom.transformedScale, boxWidth, scatter, points)
+
+            self.bounds = null
+            self.limit = DEFAULT_LIMIT
+            self.updatePreprocessor()
         }
 
         document.addEventListener('keydown', e => {

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

@@ -3,6 +3,7 @@ from Standard.Base import all
 import Standard.Table.Data.Column
 import Standard.Table.Data.Table
 import Standard.Visualization.Helpers
+from Standard.Base.Data.Index_Sub_Range import Sample
 
 ## PRIVATE
 
@@ -133,23 +134,63 @@ Table.Table.axes self =
 
 ## PRIVATE
 Vector.Vector.point_data : Vector -> Object
-Vector.Vector.point_data self =
-        self.map_with_index <| i-> elem->
-            Json.from_pairs [[X.name,i],[Y.name,elem]]
+Vector.Vector.point_data self  =
+    self.map_with_index <| i-> elem->
+        Json.from_pairs [[X.name,i],[Y.name,elem]]
 
 ## PRIVATE
-json_from_table : Table -> Json
-json_from_table table =
-    data = table.point_data
+bound_data bounds data = case bounds of
+    Nothing -> data
+    _ ->
+        min_x = bounds.at 0
+        min_y = bounds.at 1
+        max_x = bounds.at 2
+        max_y = bounds.at 3
+
+        data.filter <| datum->
+            x = datum.get "x" . unwrap
+            y = datum.get "y" . unwrap
+
+            min_x<=x && x<=max_x && min_y<=y && y<=max_y
+
+type Extreme min_x max_x min_y max_y
+
+## PRIVATE
+limit_data limit data = case limit of
+    Nothing -> data
+    _ -> if ((data.length <= limit) || (data.length == 0)) then data else
+        x datum = (datum.get "x").unwrap
+        y datum = (datum.get "y").unwrap
+
+        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
+
+        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 + data.take (Sample (limit - extreme.length))
+
+## PRIVATE
+json_from_table : Table -> [Int]|Nothing -> Int|Nothing -> Json
+json_from_table table bounds limit =
+    data = table.point_data |> bound_data bounds |> limit_data limit
     axes = table.axes
     Json.from_pairs <| [[data_field,data], [axis_field, axes]]
 
 ## PRIVATE
-json_from_vector : Vector Any -> Json
-json_from_vector vec =
-    data = [data_field, vec.point_data]
+json_from_vector : Vector Any -> [Int]|Nothing -> Int|Nothing -> Json
+json_from_vector vec bounds limit =
+    data = vec.point_data |> bound_data bounds |> limit_data limit
     axes = [axis_field, Nothing]
-    Json.from_pairs [data, axes]
+    Json.from_pairs <| [[data_field, data], axes]
 
 ## PRIVATE
 
@@ -160,12 +201,12 @@ json_from_vector vec =
    Arguments:
    - value: the value to be visualized.
 process_to_json_text : Any -> Text
-process_to_json_text value =
+process_to_json_text value bounds=Nothing limit=Nothing =
     json = case value of
-        Column.Column _ -> json_from_table  value.to_table
-        Table.Table _   -> json_from_table  value
-        Vector.Vector _ -> json_from_vector value
-        _               -> json_from_vector value.to_vector
+        Column.Column _ -> json_from_table  value.to_table bounds limit
+        Table.Table _   -> json_from_table  value bounds limit
+        Vector.Vector _ -> json_from_vector value bounds limit
+        _               -> json_from_vector value.to_vector bounds limit
 
     json.to_text
 

test/Visualization_Tests/src/Scatter_Plot_Spec.enso

@@ -10,8 +10,7 @@ import Standard.Test
 import project
 
 spec =
-    expect value axis_expected_text data_expected_text =
-        text = Scatter_Plot.process_to_json_text value
+    expect_text text axis_expected_text data_expected_text =
         json = Json.parse text
         json.fields.keys.should_equal ['axis','data']
 
@@ -20,6 +19,10 @@ spec =
         expected_result        = Json.from_pairs [expected_axis_labels, expected_data_pair]
         json.should_equal expected_result
 
+    expect value axis_expected_text data_expected_text =
+        text = Scatter_Plot.process_to_json_text value
+        expect_text text axis_expected_text data_expected_text
+
     index = Scatter_Plot.index_name
     axis label = Json.from_pairs [['label',label]]
     labels x y = Json.from_pairs [['x', axis x], ['y', axis y]] . to_text
@@ -70,6 +73,17 @@ spec =
             table = Table.from_rows header [row_1, row_2]
             expect table (labels 'x' 'y') '[{"size":40,"x":11,"y":10},{"size":50,"x":21,"y":20}]'
 
+        Test.specify "provided only recognized columns within bounds" <|
+            header = ['x', 'y' , 'bar' , 'size']
+            row_1 =  [1  , 1   , '11'  , 30    ]
+            row_2 =  [11 , 10  , 'aa'  , 40    ]
+            row_3 =  [21 , 20  , 'bb'  , 50    ]
+            row_4 =  [31 , 30  , 'cc'  , 60    ]
+            table = Table.from_rows header [row_1, row_2, row_3, row_4]
+            bounds = [0,5,25,25]
+            text = Scatter_Plot.process_to_json_text table bounds
+            expect_text text (labels 'x' 'y') '[{"size":40,"x":11,"y":10},{"size":50,"x":21,"y":20}]'
+
         Test.specify "used specified numeric index for x if missing 'x' column from table" <|
             header = [ 'y' , 'foo', 'bar', 'baz' , 'size']
             row_1 =  [ 10  , 'aa' , 12   , 14    , 40    ]
@@ -96,10 +110,36 @@ spec =
             vector = [0,10,20]
             expect vector no_labels '[{"x":0,"y":0},{"x":1,"y":10},{"x":2,"y":20}]'
 
+        Test.specify "limit the number of elements" <|
+            vector = [0,10,20,30]
+            text = Scatter_Plot.process_to_json_text vector limit=2
+            json = Json.parse text
+            json.fields.keys.should_equal ['axis','data']
+            data = json.fields.get 'data'
+            data.unwrap.length . should_equal 2
+
+
+        Test.specify "limit the number of squared elements" <|
+            vector = (-15).up_to 15 . map (x -> x * x)
+            text = Scatter_Plot.process_to_json_text vector limit=10
+            json = Json.parse text
+            json.fields.keys.should_equal ['axis','data']
+            data = (json.fields.get 'data') . unwrap
+            data.length . should_equal 10
+            (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]
+            bounds = [0,5,10,25]
+            text = Scatter_Plot.process_to_json_text vector bounds
+            expect_text text no_labels '[{"x":1,"y":10},{"x":2,"y":20}]'
+
         Test.specify "using indices for x if given a column" <|
             column = Column.from_vector 'some_col' [10,2,3]
             expect column (labels 'index' 'some_col') '[{"x":0,"y":10},{"x":1,"y":2},{"x":2,"y":3}]'
 
         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