How to use map_values

[MikaelElkiaer]

I am having some trouble with the use of map_values.
One thing I don't understand, and have come to suspect is a bug, is an apparent loss of keys.

I expected this query to be equivalent to an identity function, but the result surprises me.

$ yq 'map_values(.)' <<< "{a: {b: c}}"
{a: {}}

However, by adding a seemingly superfluous | to_entries | from_entries it behaves as I would expect.

$ yq 'map_values(. | to_entries | from_entries)' <<< "{a: {b: c}}"
{a: {b: c}}

[MikaelElkiaer]

I have a simple task I want to do with this - create a docker-compose.override.yml with just the image keys.

I can do this by

yq '. | with_entries(select(.key=="services")) | .services as $s | .services = $s | map_values(. | to_entries | from_entries | map_values(pick(["image"])))' docker-compose.yml > docker-compose.override.yml

but both the |to_entries|from_entries as well as the as $s parts seem like they should not be necessary here.

[mikefarah]

Yep that is a bug in an older version of yq - please grab the latest and try again 👍🏼

[MikaelElkiaer]

Awesome, thanks!