Set::distinctBy(), Stream::distinctBy() added and tested.

src/Set.php

@@ -44,6 +44,35 @@ public static function distinct(iterable $data, bool $strict = true): \Generator
         }
     }
 
+    /**
+     * Iterate only the distinct elements using $compareBy function for getting comparable value.
+     *
+     * Supports only strict-type comparisons:
+     *  - scalars: compares strictly by type
+     *  - objects: always treats different instances as not equal to each other
+     *  - arrays: compares serialized
+     *
+     * @template T
+     *
+     * @param iterable<T> $data
+     * @param callable $compareBy
+     *
+     * @return \Generator<T>
+     */
+    public static function distinctBy(iterable $data, callable $compareBy): \Generator
+    {
+        $map = [];
+
+        foreach ($data as $datum) {
+            $hash = UniqueExtractor::getString($compareBy($datum), true);
+
+            if (!isset($map[$hash])) {
+                $map[$hash] = true;
+                yield $datum;
+            }
+        }
+    }
+
     /**
      * Iterates the intersection of iterables in strict type mode.
      *

src/Stream.php

@@ -667,6 +667,28 @@ public function distinct(bool $strict = true): self
         return $this;
     }
 
+    /**
+     * Filter out elements from the iterable source only returning unique elements.
+     *
+     * Using $compareBy function for getting comparable value.
+     *
+     * Supports only strict-type comparisons:
+     *  - scalars: compares strictly by type
+     *  - objects: always treats different instances as not equal to each other
+     *  - arrays: compares serialized
+     *
+     * @param callable $compareBy
+     *
+     * @return $this
+     *
+     * @see Single::distinctBy()
+     */
+    public function distinctBy(callable $compareBy): self
+    {
+        $this->iterable = Set::distinctBy($this->iterable, $compareBy);
+        return $this;
+    }
+
     /**
      * Cycle through the elements of iterable source sequentially forever
      *