pandas-dev/pandas · error · ValueError

Cannot divide vectors with unequal lengths

Error message

Cannot divide vectors with unequal lengths

What it means

Raised by _cast_divlike_op when dividing a timedelta array by another array of differing length. Lengths must match for elementwise division; mismatched vectors are rejected explicitly.

Source

Thrown at pandas/core/arrays/timedeltas.py:660

            if op in [roperator.rtruediv, roperator.rfloordiv]:
                raise TypeError(
                    f"Cannot divide {type(other).__name__} by {type(self).__name__}"
                )

            if lib.is_float(other):
                # GH#43178: raise instead of silently saturating on overflow
                self._check_float_div_overflow(other)
            result = op(self._ndarray, other)
            return type(self)._simple_new(result, dtype=result.dtype)

    def _cast_divlike_op(self, other):
        if not hasattr(other, "dtype"):
            # e.g. list, tuple
            other = np.array(other)

        if len(other) != len(self):
            raise ValueError("Cannot divide vectors with unequal lengths")
        return other

    def _vector_divlike_op(self, other, op) -> np.ndarray | Self:
        """
        Shared logic for __truediv__, __floordiv__, and their reversed versions
        with timedelta64-dtype ndarray other.
        """
        other_arr = np.asarray(other)
        if other_arr.dtype.kind == "f" and op in [operator.truediv, operator.floordiv]:
            # GH#43178: raise instead of silently saturating on overflow
            self._check_float_div_overflow(other_arr)

        # Let numpy handle it
        result = op(self._ndarray, other_arr)

        if (is_integer_dtype(other.dtype) or is_float_dtype(other.dtype)) and op in [
            operator.truediv,
            operator.floordiv,

View on GitHub (pinned to 71959b8cb9)

Solutions

1. Align indices/lengths via reindex before dividing.
2. Use a scalar divisor if all elements share the same scale.
3. Verify len(other) == len(self) and document the expectation.

Example fix

// before
out = td_series / other_series  # mismatched length

// after
other = other_series.reindex(td_series.index)
out = td_series / other

assert len(td) == len(other), f'vector length mismatch: {len(td)} vs {len(other)}'

def div_lengths_match(a, b) -> bool:
    return len(a) == len(b)

try:
    out = td / other
except ValueError as e:
    if 'unequal lengths' in str(e):
        other = other.reindex(td.index) if hasattr(other, 'reindex') else other[:len(td)]
        out = td / other
    else:
        raise

When it happens

Trigger: `td_array / np.array([...])` where lengths differ; `td_series / other_series` with different index lengths and no alignment.

Common situations: Index misalignment after filter/merge; subsetting one operand but not the other; passing arrays from different sources.

Related errors

• Cannot multiply with unequal lengths
• Function did not transform
• Values resolution does not match dtype.
• Must provide freq argument if no data is supplied
• Of the four parameters: start, end, periods, and freq, exact

AI-assisted analysis of pandas-dev/pandas@71959b8cb9 (2026-08-07). Data as JSON: /api/errors/2346f26683cd4119. Report an issue: GitHub.