What causes "node at path [%v] is not an array (it's a %v)" in mikefarah/yq?

Select the array first: `.items | reverse` instead of `reverse` on the whole map.

node at path [%v] is not an array (it's a %v)

Error message

node at path [%v] is not an array (it's a %v)

What it means

The `reverse` operator only works on arrays (sequence nodes). When a matched candidate is not a SequenceNode, yq returns this error naming the node's path and tag, so you know exactly which node failed. Note it returns the original context alongside the error, so no partial results are produced for that expression run.

Source

Thrown at pkg/yqlib/operator_reverse.go:15

package yqlib

import (
	"container/list"
	"fmt"
)

func reverseOperator(_ *dataTreeNavigator, context Context, _ *ExpressionNode) (Context, error) {
	results := list.New()

	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
		candidate := el.Value.(*CandidateNode)

		if candidate.Kind != SequenceNode {
			return context, fmt.Errorf("node at path [%v] is not an array (it's a %v)", candidate.GetNicePath(), candidate.Tag)
		}

		reverseList := candidate.CreateReplacementWithComments(SequenceNode, "!!seq", candidate.Style)
		reverseContent := make([]*CandidateNode, len(candidate.Content))

		for i, originalNode := range candidate.Content {
			reverseContent[len(candidate.Content)-i-1] = originalNode
		}
		reverseList.AddChildren(reverseContent)
		results.PushBack(reverseList)

	}

	return context.ChildContext(results), nil

}

View on GitHub (pinned to 8b5af0694b)

Solutions

Select the array first: `.items | reverse` instead of `reverse` on the whole map.
If reversing map keys, use `keys | reverse` and then re-map, e.g. `to_entries | reverse | from_entries`.
Guard with `select(tag == "!!seq") | reverse` to only reverse arrays.
Use the path in the error to locate and fix the offending node or expression.

Example fix

// before
yq 'reverse' file.yml            # root is a map
// after
yq '.items | reverse' file.yml

Defensive patterns

Strategy: type-guard

Validate before calling

yq -e 'tag == "!!seq"' <<< "$node" || echo "reverse requires an array"

Type guard

isSeq() { [ "$(yq 'tag == "!!seq"' <<< "$1")" = "true" ]; }

Try / catch

out=$(yq 'select(tag == "!!seq") | reverse' file.yml 2>&1) || { echo "$out"; echo "use to_entries | reverse | from_entries for maps"; }

Prevention

Select the array before reversing: .items | reverse.
Reverse map key order with keys | reverse or to_entries | reverse | from_entries.
Guard multi-doc pipelines with select(tag == "!!seq").
Use the path in the error message to locate the non-array node.

When it happens

Trigger: `yq 'reverse'` on a document whose root is a map or scalar; `reverse` applied to a map-valued key like `.myMap | reverse`; multi-document input where one document is not an array.

Common situations: Reversing a map by mistake (expecting key order reversal — use `keys | reverse` or `to_entries` instead); schema changes turning an array into an object; selecting the parent container instead of the array field.

Related errors

AI-assisted analysis of mikefarah/yq@8b5af0694b (2026-09-05). Data as JSON: /api/errors/50f65d4fdd2221d4. Report an issue: GitHub.