JEP-18 Grouping (#80)

Author: springcomp

src/jmespath.net/Functions/GroupByFunction.cs

@@ -0,0 +1,68 @@
+using DevLab.JmesPath.Utils;
+using Newtonsoft.Json.Linq;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace DevLab.JmesPath.Functions
+{
+    public class GroupByFunction : ByFunction
+    {
+        public GroupByFunction()
+            : base("group_by")
+        {
+        }
+
+        public override void Validate(params JmesPathFunctionArgument[] args)
+        {
+            base.Validate(args);
+
+            System.Diagnostics.Debug.Assert(args.Length == 2);
+            System.Diagnostics.Debug.Assert(args[0].IsToken);
+            System.Diagnostics.Debug.Assert(args[1].IsExpressionType);
+
+            var array = (JArray)args[0].Token;
+            if (array.Any(i => i.Type != JTokenType.Object))
+                throw new Exception($"Error: invalid-type, function {Name} expects its first argument to be an array of objects.");
+        }
+        public override JToken Execute(params JmesPathFunctionArgument[] args)
+        {
+            System.Diagnostics.Debug.Assert(args.Length == 2);
+            System.Diagnostics.Debug.Assert(args[0].IsToken);
+            System.Diagnostics.Debug.Assert(args[1].IsExpressionType);
+
+            var array = (JArray)args[0].Token;
+            var expression = args[1].Expression;
+
+            var dictionary = new Dictionary<string, IList<JToken>>();
+
+            foreach (var element in array)
+            {
+                string key = "";
+
+                var token = expression.Transform(element).AsJToken();
+                if (token != JTokens.Null)
+                {
+                    var tokenType = token.GetTokenType();
+                    if (tokenType != "string")
+                        throw new Exception($"Error: invalid-type, function {Name} expects its second expression-type argument to evaluate to a 'string' value but received '{tokenType}' {token} instead.");
+
+                    key = token.Value<string>();
+                    AddElement(dictionary, key, element);
+                }
+            }
+
+            var properties = dictionary.Select(kvp => new JProperty(kvp.Key, kvp.Value));
+
+            return new JObject(properties);
+        }
+
+        private static void AddElement(IDictionary<string, IList<JToken>> dictionary, string key, JToken element)
+        {
+            if (!dictionary.ContainsKey(key))
+                dictionary[key] = new List<JToken>();
+
+            dictionary[key].Add(element);
+        }
+    }
+}

src/jmespath.net/Functions/JmesPathFunctionFactory.cs

@@ -29,6 +29,7 @@ private JmesPathFunctionFactory(IScopeParticipant scopes)
                 .Register<FindFirstFunction>()
                 .Register<FindLastFunction>()
                 .Register<FloorFunction>()
+                .Register<GroupByFunction>()
                 .Register<JoinFunction>()
                 .Register<LengthFunction>()
                 .Register<LowerFunction>()

tools/jmespathnet.compliance/regression/group_by_function.json

@@ -0,0 +1,18 @@
+[
+  {
+    "given": {
+      "items": [
+        { "spec": { "nodeNumber":  1, "nodeName": "node_01", "other": "values_01" } },
+        { "spec": { "nodeNumber":  2, "nodeName": "node_02", "other": "values_02" } },
+        { "spec": { "nodeNumber":  3, "nodeName": "node_03", "other": "values_03" } },
+        { "spec": { "nodeNumber":  1, "nodeName": "node_01", "other": "values_04" } }
+      ]
+    },
+    "cases": [
+      {
+        "expression": "group_by(items, &spec.nodeNumber)",
+        "error": "invalid-type"
+      }
+    ]
+  }
+]