Added FeatureCollection.propertiesSummary() (#63)

Sources/GISTools/Algorithms/EnumerateProperties.swift

@@ -5,13 +5,34 @@ import Foundation
 
 extension FeatureCollection {
 
-    /// Enumerate all properties in the FeatureCollection with feature index..
+    /// Enumerate over all Feature properties in the FeatureCollection.
     ///
-    /// - Parameter callback: The callback function
+    /// - Parameter callback: The callback function, called for each Feature with Feature index and properties
     public func enumerateProperties(_ callback: (_ featureIndex: Int, _ properties: [String: Sendable]) -> Void)  {
         for (featureIndex, feature) in features.enumerated() {
             callback(featureIndex, feature.properties)
         }
     }
 
+    /// Creates a summary over all properties in the FeatureCollection.
+    ///
+    /// - Returns: A dictionary with all the keys found in all properties of the FeatureCollection,
+    ///            and the values are the distinct values for each key.
+    ///
+    /// - Note: All valid JSON types are `Hashable`.
+    public func propertiesSummary() -> [String: [AnyHashable]] {
+        var keyValuePairs: [(String, Set<AnyHashable>)] = []
+
+        for feature in features {
+            for (key, value) in feature.properties {
+                if let hashable = value as? AnyHashable {
+                    keyValuePairs.append((key, Set([hashable])))
+                }
+            }
+        }
+
+        return Dictionary(keyValuePairs, uniquingKeysWith: { $0.union($1) })
+            .mapValues(\.asArray)
+    }
+
 }

Sources/GISTools/Extensions/SetExtensions.swift

@@ -0,0 +1,12 @@
+import Foundation
+
+// MARK: Private
+
+extension Set {
+
+    /// Converts the Set to an Array
+    var asArray: [Element] {
+        Array(self)
+    }
+
+}

Tests/GISToolsTests/GeoJson/FeatureCollectionTests.swift

@@ -150,7 +150,7 @@ final class FeatureCollectionTests: XCTestCase {
             (2, 4, Coordinate3D(latitude: 0.0, longitude: 100.0))
         ]
 
-        var result:[(Int, Int, Coordinate3D)] = []
+        var result: [(Int, Int, Coordinate3D)] = []
         featureCollection.enumerateCoordinates { featureIndex, coordinateIndex, coordinate in
             result.append((featureIndex, coordinateIndex, coordinate))
         }
@@ -164,6 +164,39 @@ final class FeatureCollectionTests: XCTestCase {
         }
     }
 
+    func testEnumerateProperties() throws {
+        let featureCollection = try XCTUnwrap(FeatureCollection(jsonString: FeatureCollectionTests.featureCollectionJson))
+
+        let expected: [(Int, [String: Sendable])] = [
+            (0, ["prop0": "value0"]),
+            (1, ["prop0": "value0", "prop1": 0]),
+            (2, ["prop0": "value0", "prop1": ["this": "that"]])
+        ]
+
+        var result: [(Int, [String: Sendable])] = []
+        featureCollection.enumerateProperties { featureIndex, properties in
+            XCTAssertFalse(properties.isEmpty)
+            result.append((featureIndex, properties))
+        }
+
+        XCTAssertEqual(result.count, expected.count)
+
+        for (lhs, rhs) in zip(result, expected) {
+            XCTAssertEqual(lhs.0, rhs.0)
+        }
+    }
+
+    func testPropertiesSummary() throws {
+        let featureCollection = try XCTUnwrap(FeatureCollection(jsonString: FeatureCollectionTests.featureCollectionJson))
+
+        let summary = featureCollection.propertiesSummary()
+        XCTAssertEqual(summary.count, 2)
+        XCTAssertEqual(summary.keys.sorted(), ["prop0", "prop1"])
+        XCTAssertEqual(summary["prop0"], ["value0"])
+        XCTAssertTrue(summary["prop1"]!.contains(0))
+        XCTAssertTrue(summary["prop1"]!.contains(["this": "that"]))
+    }
+
     func testEncodable() throws {
         let featureCollection = try XCTUnwrap(FeatureCollection(jsonString: FeatureCollectionTests.featureCollectionJson))