diff --git a/sqlite/util/filter_valid_groups.py b/sqlite/util/filter_valid_groups.py
new file mode 100644
index 0000000000..ea4a54d042
--- /dev/null
+++ b/sqlite/util/filter_valid_groups.py
@@ -0,0 +1,104 @@
+# filter_valid_groups.py
+from typing import Set, List, Callable
+
+SampleUid = str
+SampleType = str
+Group = Set[SampleUid]  # Original group: set of sample UIDs
+
+
+def filter_valid_groups(
+    groups: List[Group], sample_type_getter: Callable[[SampleUid], SampleType]
+) -> List[Group]:
+    """
+    Filter valid groups: all samples in a group must have the same type.
+
+    Args:
+        groups: List of original groups, each a set of sample UIDs.
+        sample_type_getter: Function that returns the type string for a given sample UID.
+
+    Returns:
+        List of valid groups, each still as a set of sample UIDs (no wrapping).
+    """
+    valid_groups = []
+    for group in groups:
+        # Collect the types of all samples in the group
+        types_in_group = {sample_type_getter(uid) for uid in group}
+        # Keep the group only if the set of types has exactly one element
+        if len(types_in_group) == 1:
+            valid_groups.append(group)
+    return valid_groups
+
+
+if __name__ == "__main__":
+    # ------------------------------------------------------------
+    # Test cases
+    # ------------------------------------------------------------
+
+    # Sample type mapping (simulates a database)
+    sample_types = {
+        "s1": "typeA",
+        "s2": "typeA",
+        "s3": "typeB",
+        "s4": "typeB",
+        "s5": "typeC",
+        "s6": "typeC",
+        "s7": "typeA",
+        "s8": "typeB",
+        "empty_sample": "typeX",
+    }
+
+    def getter(uid: str) -> str:
+        return sample_types[uid]
+
+    # Test 1: All groups valid
+    groups1 = [{"s1", "s2"}, {"s3", "s4"}, {"s5"}]  # s5 alone is valid
+    expected1 = [{"s1", "s2"}, {"s3", "s4"}, {"s5"}]
+    result1 = filter_valid_groups(groups1, getter)
+    assert result1 == expected1, f"Test 1 failed: {result1}"
+
+    # Test 2: Mixed valid/invalid
+    groups2 = [
+        {"s1", "s2"},  # valid (typeA)
+        {"s1", "s3"},  # invalid (typeA + typeB)
+        {"s5", "s6"},  # valid (typeC)
+        {"s7", "s8"},  # invalid (typeA + typeB)
+        set(),  # empty group -> invalid (len(types)=0)
+    ]
+    expected2 = [{"s1", "s2"}, {"s5", "s6"}]
+    result2 = filter_valid_groups(groups2, getter)
+    assert result2 == expected2, f"Test 2 failed: {result2}"
+
+    # Test 3: No valid groups
+    groups3 = [{"s1", "s3"}, {"s2", "s4", "s5"}, {"s1", "s2", "s3"}]
+    expected3 = []
+    result3 = filter_valid_groups(groups3, getter)
+    assert result3 == expected3, f"Test 3 failed: {result3}"
+
+    # Test 4: Single element groups (always valid)
+    groups4 = [{"s1"}, {"s3"}, {"s5"}, {"s7"}]
+    expected4 = [{"s1"}, {"s3"}, {"s5"}, {"s7"}]
+    result4 = filter_valid_groups(groups4, getter)
+    assert result4 == expected4, f"Test 4 failed: {result4}"
+
+    # Test 5: Case sensitivity (if types are case‑sensitive)
+    sample_types_case = {"sA": "type", "sB": "TYPE"}
+
+    def getter_case(uid):
+        return sample_types_case[uid]
+
+    groups5 = [{"sA", "sB"}]  # different strings -> invalid
+    expected5 = []
+    result5 = filter_valid_groups(groups5, getter_case)
+    assert result5 == expected5, f"Test 5 failed: {result5}"
+
+    # Test 6: Large group with identical type
+    large_group = {f"x{i}" for i in range(100)}
+    # Assign same type to all members
+    for uid in large_group:
+        sample_types[uid] = "uniform"
+    groups6 = [large_group]
+    expected6 = [large_group]
+    result6 = filter_valid_groups(groups6, getter)
+    assert result6 == expected6, f"Test 6 failed: {result6}"
+
+    print("All tests passed.")