Feature: `sort_keys(.) | reverse` or `sort_keys_reverse(.)`

[polarathene]

Please describe your feature request.

A reverse sort on a map by it's keys. The opposite of sort_keys(). I needed this to preserve YAML anchors before referenced as aliases.

EDIT: This could be closed as the feature was previously requested and rejected in 2022, but user advised to convert map into entries, sort + reverse, then convert list back to map. Docs could maybe be improved for an example of reverse map keys use-case?

Describe the solution you'd like

If we have data.yml like:

name: example

x-override: &override
  command: from-fragment

services:
  base:
    command: before-merge
    image: localhost/hello-world

  ext:
    <<: *override
    extends:
      service: base

And we run a command:

yq 'sort_keys(.) | reverse' data.yml

or

yq 'sort_keys_reverse(.)' data.yml

it could output:

x-override: &override
  command: from-fragment

services:
  base:
    command: before-merge
    image: localhost/hello-world

  ext:
    <<: *override
    extends:
      service: base

name: example

Describe alternatives you've considered

See follow-up comment for more details, but these are valid alternative approaches:

yq 'to_entries | sort_by(.key) | reverse | from_entries' file.yaml

yq '(. *= load("b.yaml")) | sort_by(key | select(. != "x-*") )' a.yaml

yq '. *= (load("`b.yaml") | explode(.)) | pick(keys | filter(. != "x-*"))' a.yaml

Additional context

Reference - Related docs

https://mikefarah.gitbook.io/yq/operators/sort#sort-a-map-by-keys

---

https://mikefarah.gitbook.io/yq/operators/sort-keys#sort-keys-of-map

[polarathene]

In my specific case I was merging multiple Docker Compose compose.yaml files, which advise storing content with YAML anchors at the root-level with an x- prefix (which their parser ignores when validating schema). It's important that these are declared near the top before referencing with YAML aliases, as the YQ docs describe as a caveat for sort_keys(.).

reverse() sorting would have worked, but it expects a list, not a map 😒

@mikefarah did respond in 2022 to a feature request for reversing sort_keys(.), stating they'd document a workaround to convert the map into a list and back after reversing, but I don't recall coming across that in the sort() / sort_keys() docs:

yq 'to_entries | sort_by(.key) | reverse | from_entries' file.yaml

Which isn't too bad of an approach I guess?

---

After exploring the docs more, I realized in my situation I could instead use sort_by() with a condition on the key prefix via select() and a glob pattern:

yq '(. *= load("b.yaml")) | sort_by(key | select(. != "x-*") )' a.yaml

Or, again due to the use-case since Docker Compose supports another feature that can import multiple YAML files, it resolves YAML aliases before merging documents, so I could mimic that with YQ via explode(), I'd just need to remove the x-* keys after as they became redundant:

yq '. *= (load("`b.yaml") | explode(.)) | pick(keys | filter(. != "x-*"))' a.yaml

I had seen another example of using pick() from 2022 comment by @mikefarah again, which demonstrated how to order keys if you needed a fixed order:

yq '.myMap |= pick( (load(my_map_key_order.yaml) + keys) | unique )' file.yml

Some follow-up comments show variations on that. I think with my example above, I could have used keys | reverse, and either filtered like shown or followed up with a del() to remove the x-* keys.

---

For reference my more advanced variant for compose.yaml with list of YAML files to merge (via include.path[]), I settled on this yq command for a naive implementation of docker compose config, which doesn't introduce extra noise to the output that docker compose config does:

yq '. *= (
  # Load all paths in order, merge YAML fragments (`explode`)
  # and remove any extension keys (`x-` prefix) via filtering keys with `pick`,
  # then `ireduce` will merge the resolved documents, preferring newer fields.
  # `ireduce` is after processing each loaded YAML file (scope wrapped via parens)
  # that result is then merged into the original `compose.yaml` input,
  # and the `include` top-level key is removed.
    ( .include[].path[] | load(.) | explode(.) | pick(keys | filter(. != "x-*")) )
    | . as $item ireduce ({}; . * $item )
  )
  | del(.include)
  # Sort all keys (in all maps) lexicographically,
  # then use `pick` with top-level key order that matches the sort Docker Compose uses.
  # Any remaining keys are retained via `+ keys` and `unique` (prefer prepended)
  | sort_keys(..) | pick(
    ["name", "services", "networks", "volumes", "configs"] + keys
    | unique
  )
  # Strip away all YAML comments:
  | ... comments=""
' compose.yaml