What causes "Child arrays do not have even length" in cakephp/cakephp?

Normalize all rows to the same length before transposing (pad with null or truncate)

cakephp/cakephp · error · LogicException

Child arrays do not have even length

Error message

Child arrays do not have even length

What it means

transpose() swaps rows and columns of a collection of arrays, like a matrix transpose. It requires every child array to have the same length; the first element defines the expected length and any row with a different count triggers this LogicException.

Solutions

Normalize all rows to the same length before transposing (pad with null or truncate)
Filter out rows that don't match the expected length: ->filter(fn ($r) => count($r) === $expected)
Fix the data source so every row has the same number of fields
Wrap in try-catch (LogicException) and handle ragged input separately

Example fix

// before
$t = $collection->transpose(); // [[1,2],[3,4,5]]
// after
$max = max($collection->map(fn ($r) => count($r))->toList());
$normalized = $collection->map(fn ($r) => $r + array_fill(count($r), $max - count($r), null));
$t = $normalized->transpose();

Defensive patterns

Strategy: validation

Validate before calling

$rows = $collection->toList();
if (count($rows) > 1 && count(array_unique(array_map('count', $rows))) > 1) {
    throw new \UnexpectedValueException('Ragged rows: cannot transpose');
}

Type guard

function isRectangular(array $rows): bool
{
    if (!$rows) { return true; }
    $len = count(reset($rows));
    return count($rows) === 1 || count(array_unique(array_map('count', $rows))) === 1;
}

Try / catch

try {
    $t = $collection->transpose();
} catch (\LogicException $e) {
    $t = normalizeRows($collection)->transpose();
}

Prevention

Pad or trim rows to a uniform length before transposing
Validate source data (e.g. CSV parsing) rejects rows with missing fields
Use array_pad/arrayslice normalization as a standard pre-step
Test transpose with edge cases: empty first row, single row, single column

When it happens

Trigger: Calling ->transpose() where elements are arrays of unequal length, e.g. [[1,2,3],[4,5]]; first element is empty while others are not (or vice versa).

Common situations: Transposing CSV-like rows where some rows have missing trailing fields; ragged API response rows; forgetting to normalize/pad records before transposing.

Related errors

AI-assisted analysis of cakephp/cakephp@1128eba9b0 (2026-09-12). Data as JSON: /api/errors/31be4b57b98ee500. Report an issue: GitHub.

Appendix: source

Thrown at src/Collection/CollectionTrait.php:1194

        return $this->newCollection($result); // @phpstan-ignore return.type
    }

    /**
     * {@inheritDoc}
     *
     * @return \Cake\Collection\CollectionInterface<int, array<mixed>>
     * @throws \LogicException
     */
    public function transpose(): CollectionInterface
    {
        $arrayValue = $this->toList();
        /** @phpstan-ignore argument.type (transpose requires array values) */
        $length = count(current($arrayValue));
        $result = [];
        foreach ($arrayValue as $row) {
            /** @phpstan-ignore argument.type (transpose requires array values) */
            if (count($row) !== $length) {
                throw new LogicException('Child arrays do not have even length');
            }
        }

        for ($column = 0; $column < $length; $column++) {
            $result[] = array_column($arrayValue, $column);
        }

        return $this->newCollection($result); // @phpstan-ignore return.type
    }

    /**
     * @inheritDoc
     */
    public function count(): int
    {
        $traversable = $this->optimizeUnwrap();

        if (is_array($traversable)) {

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