How to extract common `yq` to keep script DRY? - yq

Question

I have the following (modified from from https://stackoverflow.com/a/70152440/807037):
yq eval-all '
.clusters = (
(
(.clusters[] | {.name: .}) as $item ireduce ({}; . * $item)
) as $uniqueMap |
( $uniqueMap | to_entries | .[]) as $item ireduce([]; . + $item.value)
) |
.contexts = (
(
(.contexts[] | {.name: .}) as $item ireduce ({}; . * $item)
) as $uniqueMap |
( $uniqueMap | to_entries | .[]) as $item ireduce([]; . + $item.value)
) |
select(fi == 0)' konfig monfig
How can the following common code be extracted so as to keep the script DRY:
.«KEY» = (
(
(.«KEY»[] | {.name: .}) as $item ireduce ({}; . * $item)
) as $uniqueMap |
( $uniqueMap | to_entries | .[]) as $item ireduce([]; . + $item.value)
)
Input files:
# konfig
apiVersion: apiVersion-keep
clusters:
- cluster:
certificate-authority-data: cad-0
server: server-0
name: name-0
- cluster:
certificate-authority-data: cad-1-discard
server: server-1-discard
name: name-1
- cluster:
certificate-authority-data: cad-2
server: server-2
name: name-2
contexts:
- context:
cluster: cluster-0
user: user-0
name: name-0
- context:
cluster: cluster-1-discard
user: user-1-discard
name: name-1
- context:
cluster: cluster-2
user: user-2
name: name-2
current-context: name-keep
# monfig
apiVersion: apiVersion-discard
clusters:
- cluster:
certificate-authority-data: cad-1-keep
server: server-1-keep
name: name-1
contexts:
- context:
cluster: cluster-1-keep
user: user-1-keep
name: name-1
current-context: name-discard
Expected:
apiVersion: apiVersion-keep
clusters:
- cluster:
certificate-authority-data: cad-0
server: server-0
name: name-0
- cluster:
certificate-authority-data: cad-1-keep
server: server-1-keep
name: name-1
- cluster:
certificate-authority-data: cad-2
server: server-2
name: name-2
contexts:
- context:
cluster: cluster-0
user: user-0
name: name-0
- context:
cluster: cluster-1-keep
user: user-1-keep
name: name-1
- context:
cluster: cluster-2
user: user-2
name: name-2
current-context: name-keep

Answer 1

The issue is a little trickier than it appears because a use case for |= is updating each matching left hand side node with respect to itself. .clusters results in two nodes (as with .contexts) and each of those nodes is updated independently. yq doesn't know to group the nodes together. After playing around a little I got this to work:
./yq eval-all '
. ref $r |
with( ("clusters", "contexts");
$r[.] = (
(
($r[.] | .[] | {.name: .}) as $item ireduce ({}; . * $item)
) as $uniqueMap |
( $uniqueMap | to_entries | .[]) as $item ireduce([]; . + $item.value)
)
) | select(fi==0)' file1.yaml file2.yaml
Explanation:
. ref $r Create a reference to the root context, called $r. This matches the top level nodes (file1 and file2).
Using the with operator, I can parameterise the merge expression against $r, passing in the two paths that need to be merged. Each path is run against the root context $r in $r[.].
Hope that makes sense!
Disclaimer: I wrote yq

Answer 2

Generally speaking (due to missing sample data), you can use the update operator |= (available since v4.3.0), enabling you to address by context . on the RHS. Then, as the absolute context only appears on the LHS, you can just list at once all contexts you want this to be applied to.
(.clusters, .contexts) |= ( .[] | ... )