introduce clusterProperties option for aggregating cluster properties

debug/cluster.html

@@ -31,15 +31,20 @@
         "type": "geojson",
         "data": "/test/integration/data/places.geojson",
         "cluster": true,
-        "clusterRadius": 50
+        "clusterRadius": 50,
+        "clusterProperties": {
+            "max": ["max", 0, ["get", "scalerank"]],
+            "sum": ["+", 0, ["get", "scalerank"]],
+            "has_island": ["any", false, ["==", ["get", "featureclass"], "island"]]
+        }
     });
     map.addLayer({
         "id": "cluster",
         "type": "circle",
         "source": "geojson",
         "filter": ["==", "cluster", true],
         "paint": {
-            "circle-color": "rgba(0, 200, 0, 1)",
+            "circle-color": ["case", ["get", "has_island"], "orange", "rgba(0, 200, 0, 1)"],
             "circle-radius": 20
         }
     });
@@ -49,7 +54,7 @@
         "source": "geojson",
         "filter": ["==", "cluster", true],
         "layout": {
-            "text-field": "{point_count}",
+            "text-field": "{point_count} ({max})",
             "text-font": ["Open Sans Semibold", "Arial Unicode MS Bold"],
             "text-size": 12,
             "text-allow-overlap": true,

src/source/geojson_source.js

@@ -139,7 +139,8 @@ class GeoJSONSource extends Evented implements Source {
                 extent: EXTENT,
                 radius: (options.clusterRadius || 50) * scale,
                 log: false
-            }
+            },
+            clusterProperties: options.clusterProperties
         }, options.workerOptions);
     }
 

src/source/geojson_worker_source.js

@@ -10,6 +10,7 @@ import Supercluster from 'supercluster';
 import geojsonvt from 'geojson-vt';
 import assert from 'assert';
 import VectorTileWorkerSource from './vector_tile_worker_source';
+import { createExpression } from '../style-spec/expression';
 
 import type {
     WorkerTileParameters,
@@ -171,7 +172,7 @@ class GeoJSONWorkerSource extends VectorTileWorkerSource {
 
                 try {
                     this._geoJSONIndex = params.cluster ?
-                        new Supercluster(params.superclusterOptions).load(data.features) :
+                        new Supercluster(getSuperclusterOptions(params)).load(data.features) :
                         geojsonvt(data, params.geojsonVtOptions);
                 } catch (err) {
                     return callback(err);
@@ -293,4 +294,57 @@ class GeoJSONWorkerSource extends VectorTileWorkerSource {
     }
 }
 
+function getSuperclusterOptions({superclusterOptions, clusterProperties}) {
+    if (!clusterProperties || !superclusterOptions) return superclusterOptions;
+
+    const initialValues = {};
+    const mapExpressions = {};
+    const reduceExpressions = {};
+    const globals = {accumulated: null};
+    const feature = {properties: null};
+    const propertyNames = Object.keys(clusterProperties);
+
+    for (const key of propertyNames) {
+        const [operator, initialExpression, mapExpression] = clusterProperties[key];
+        initialValues[key] = createClusterExpression(key, initialExpression).evaluate(globals);
+        mapExpressions[key] = createClusterExpression(key, mapExpression);
+        reduceExpressions[key] = createClusterExpression(key, [operator, ['accumulated'], ['get', key]]);
+    }
+
+    superclusterOptions.initial = () => {
+        const properties = {};
+        for (const key of propertyNames) {
+            properties[key] = initialValues[key];
+        }
+        return properties;
+    };
+    superclusterOptions.map = (pointProperties) => {
+        feature.properties = pointProperties;
+        const properties = {};
+        for (const key of propertyNames) {
+            properties[key] = mapExpressions[key].evaluate(globals, feature);
+        }
+        return properties;
+    };
+    superclusterOptions.reduce = (accumulated, clusterProperties) => {
+        feature.properties = clusterProperties;
+        for (const key of propertyNames) {
+            globals.accumulated = accumulated[key];
+            accumulated[key] = reduceExpressions[key].evaluate(globals, feature);
+        }
+    };
+
+    return superclusterOptions;
+}
+
+function createClusterExpression(key, expression) {
+    const parsed = createExpression(expression, {});
+    if (parsed.result === 'success') {
+        return parsed.value;
+    }
+    /* eslint no-warning-comments: 0 */
+    // TODO proper error handling
+    console.log(`Error: ${parsed.value.map(e => e.message).join('; ')}`);
+}
+
 export default GeoJSONWorkerSource;

src/style-spec/expression/definitions/index.js

@@ -201,6 +201,11 @@ CompoundExpression.register(expressions, {
         [],
         (ctx) => ctx.globals.lineProgress || 0
     ],
+    'accumulated': [
+        ValueType,
+        [],
+        (ctx) => ctx.globals.accumulated
+    ],
     '+': [
         NumberType,
         varargs(NumberType),

src/style-spec/expression/parsing_context.js

@@ -226,5 +226,5 @@ function isConstant(expression: Expression) {
     }
 
     return isFeatureConstant(expression) &&
-        isGlobalPropertyConstant(expression, ['zoom', 'heatmap-density', 'line-progress', 'is-supported-script']);
+        isGlobalPropertyConstant(expression, ['zoom', 'heatmap-density', 'line-progress', 'accumulated', 'is-supported-script']);
 }

src/style-spec/reference/v8.json

@@ -373,6 +373,10 @@
       "type": "number",
       "doc": "Max zoom on which to cluster points if clustering is enabled. Defaults to one zoom less than maxzoom (so that last zoom features are not clustered)."
     },
+    "clusterProperties": {
+      "type": "*",
+      "doc": "TODO cluster properties"
+    },
     "lineMetrics": {
       "type": "boolean",
       "default": false,

src/style-spec/types.js

@@ -121,6 +121,7 @@ export type GeoJSONSourceSpecification = {|
     "cluster"?: boolean,
     "clusterRadius"?: number,
     "clusterMaxZoom"?: number,
+    "clusterProperties"?: mixed,
     "lineMetrics"?: boolean,
     "generateId"?: boolean
 |}