chroma-core/chroma · error · TypeError

$min requires a list, got {type(ranks_data).__name__}

Error message

$min requires a list, got {type(ranks_data).__name__}

What it means

$min folds a chain of pairwise minimums over rank expressions (the counterpart of $max, used e.g. to cap scores) and expects its payload to be a list of operand dicts. Rank.from_dict raises this TypeError when the $min payload is not a list/tuple — commonly a {'left','right'} dict in the $sub/$div style.

Source

Thrown at chromadb/execution/expression/operator.py:855

            if not isinstance(ranks_data, (list, tuple)):
                raise TypeError(
                    f"$max requires a list, got {type(ranks_data).__name__}"
                )
            if len(ranks_data) < 2:
                raise ValueError(
                    f"$max requires at least 2 ranks, got {len(ranks_data)}"
                )

            ranks = [Rank.from_dict(r) for r in ranks_data]
            result = ranks[0]
            for r in ranks[1:]:
                result = result.max(r)
            return result

        elif op == "$min":
            ranks_data = data["$min"]
            if not isinstance(ranks_data, (list, tuple)):
                raise TypeError(
                    f"$min requires a list, got {type(ranks_data).__name__}"
                )
            if len(ranks_data) < 2:
                raise ValueError(
                    f"$min requires at least 2 ranks, got {len(ranks_data)}"
                )

            ranks = [Rank.from_dict(r) for r in ranks_data]
            result = ranks[0]
            for r in ranks[1:]:
                result = result.min(r)
            return result

        else:
            raise ValueError(f"Unknown rank operator: {op}")

    # Arithmetic operators
    def __add__(self, other: Union["Rank", float, int]) -> "Sum":

View on GitHub (pinned to aecdd12c8a)

Solutions

1. Use the list form: {"$min": [rank_a, {"$val": 1.0}]}
2. Convert pair dicts: {'$min': [pair['left'], pair['right']]}
3. Build in Python as rank.min(1.0).to_dict()
4. Guard: isinstance(expr['$min'], (list, tuple)) before Rank.from_dict

Example fix

# before
expr = {"$min": {"left": knn_rank, "right": {"$val": 1.0}}}

# after
expr = {"$min": [knn_rank, {"$val": 1.0}]}

def valid_min_expr(expr):
    return (
        isinstance(expr, dict) and set(expr) == {"$min"}
        and isinstance(expr["$min"], (list, tuple))
    )

if not valid_min_expr(rank_expr):
    raise ValueError(f"$min payload must be a list: {rank_expr!r}")

def is_min_expr(d) -> bool:
    return (isinstance(d, dict) and set(d) == {"$min"}
            and isinstance(d["$min"], (list, tuple)))

try:
    rank = Rank.from_dict(rank_expr)
except (TypeError, ValueError) as e:
    raise ValueError(f"invalid rank expression {rank_expr!r}: {e}") from e

When it happens

Trigger: Rank.from_dict({'$min': {'left': a, 'right': b}}) or {'$min': 1.0} anywhere in a rank expression being deserialized.

Common situations: Hand-written cap expressions where the author alternates payload conventions; generators that emit the dict shape for every binary operator; JSON adapted from a $div example.

Related errors

• $sub requires a dict with 'left' and 'right', got {type(sub_
• $mul requires a list, got {type(ranks_data).__name__}
• $div requires a dict with 'left' and 'right', got {type(div_
• $abs requires a rank dict, got {type(child_data).__name__}
• $exp requires a rank dict, got {type(child_data).__name__}

AI-assisted analysis of chroma-core/chroma@aecdd12c8a (2026-08-16). Data as JSON: /api/errors/ecc48cb7937d20a6. Report an issue: GitHub.