From 5a2eeed06680080e0a29c31ce3740740b840f0fe Mon Sep 17 00:00:00 2001
From: Willi Ballenthin <willi.ballenthin@gmail.com>
Date: Sat, 20 Jun 2026 09:52:56 +0200
Subject: [PATCH] fix Set Difference and Set Intersection preserve duplicates
 from first sample (#2286)

---
 src/core/operations/SetDifference.mjs      |  9 +++++++-
 src/core/operations/SetIntersection.mjs    |  9 +++++++-
 tests/operations/tests/SetDifference.mjs   | 22 ++++++++++++++++++++
 tests/operations/tests/SetIntersection.mjs | 24 +++++++++++++++++++++-
 4 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/src/core/operations/SetDifference.mjs b/src/core/operations/SetDifference.mjs
index dc46c079..d5ab92d3 100644
--- a/src/core/operations/SetDifference.mjs
+++ b/src/core/operations/SetDifference.mjs
@@ -75,9 +75,16 @@ class SetDifference extends Operation {
      * @returns {Object[]}
      */
     runSetDifference(a, b) {
+        const excluded = new Set(b);
+        const seen = new Set();
+
         return a
             .filter((item) => {
-                return b.indexOf(item) === -1;
+                if (excluded.has(item) || seen.has(item)) {
+                    return false;
+                }
+                seen.add(item);
+                return true;
             })
             .join(this.itemDelimiter);
     }
diff --git a/src/core/operations/SetIntersection.mjs b/src/core/operations/SetIntersection.mjs
index 7e6dbe10..423fcd4f 100644
--- a/src/core/operations/SetIntersection.mjs
+++ b/src/core/operations/SetIntersection.mjs
@@ -75,9 +75,16 @@ class SetIntersection extends Operation {
      * @returns {Object[]}
      */
     runIntersect(a, b) {
+        const included = new Set(b);
+        const seen = new Set();
+
         return a
             .filter((item) => {
-                return b.indexOf(item) > -1;
+                if (!included.has(item) || seen.has(item)) {
+                    return false;
+                }
+                seen.add(item);
+                return true;
             })
             .join(this.itemDelimiter);
     }
diff --git a/tests/operations/tests/SetDifference.mjs b/tests/operations/tests/SetDifference.mjs
index 40fac524..5836cb36 100644
--- a/tests/operations/tests/SetDifference.mjs
+++ b/tests/operations/tests/SetDifference.mjs
@@ -53,4 +53,26 @@ TestRegister.addTests([
             },
         ],
     },
+    {
+        name: "Set Difference: duplicates in first set are removed",
+        input: "red,red,blue\n\nblue",
+        expectedOutput: "red",
+        recipeConfig: [
+            {
+                op: "Set Difference",
+                args: ["\n\n", ","],
+            },
+        ],
+    },
+    {
+        name: "Set Difference: duplicates in both sets",
+        input: "1 1 2 2 3\n\n2 2 3 3",
+        expectedOutput: "1",
+        recipeConfig: [
+            {
+                op: "Set Difference",
+                args: ["\n\n", " "],
+            },
+        ],
+    },
 ]);
diff --git a/tests/operations/tests/SetIntersection.mjs b/tests/operations/tests/SetIntersection.mjs
index c9146c01..a638db4a 100644
--- a/tests/operations/tests/SetIntersection.mjs
+++ b/tests/operations/tests/SetIntersection.mjs
@@ -52,5 +52,27 @@ TestRegister.addTests([
                 args: ["z", "-"],
             },
         ],
-    }
+    },
+    {
+        name: "Set Intersection: duplicates in first set are removed",
+        input: "red,red,blue\n\nred,blue",
+        expectedOutput: "red,blue",
+        recipeConfig: [
+            {
+                op: "Set Intersection",
+                args: ["\n\n", ","],
+            },
+        ],
+    },
+    {
+        name: "Set Intersection: duplicates in both sets",
+        input: "1 1 2 2 3\n\n2 2 3 3 4",
+        expectedOutput: "2 3",
+        recipeConfig: [
+            {
+                op: "Set Intersection",
+                args: ["\n\n", " "],
+            },
+        ],
+    },
 ]);