yq/pkg/yqlib/doc/operators/multiply-merge.md

Multiply (Merge)

Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently numbers, arrays and objects are supported.

Objects and arrays - merging

Objects are merged deeply matching on matching keys. By default, array values override and are not deeply merged.

Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.

Merge Flags

You can control how objects are merged by using one or more of the following flags. Multiple flags can be used together, e.g. .a *+? .b. See examples below

• + to append arrays
• ? to only merge existing fields
• d to deeply merge arrays

Merging files

Note the use of eval-all to ensure all documents are loaded into memory.

yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml

Multiply integers

Running

yq eval --null-input '3 * 4'

will output

12

Merge objects together, returning merged result only

Given a sample.yml file of:

a:
  field: me
  fieldA: cat
b:
  field:
    g: wizz
  fieldB: dog

then

yq eval '.a * .b' sample.yml

will output

field:
  g: wizz
fieldA: cat
fieldB: dog

Merge objects together, returning parent object

Given a sample.yml file of:

a:
  field: me
  fieldA: cat
b:
  field:
    g: wizz
  fieldB: dog

then

yq eval '. * {"a":.b}' sample.yml

will output

a:
  field:
    g: wizz
  fieldA: cat
  fieldB: dog
b:
  field:
    g: wizz
  fieldB: dog

Merge keeps style of LHS

Given a sample.yml file of:

a: {things: great}
b:
  also: "me"

then

yq eval '. * {"a":.b}' sample.yml

will output

a: {things: great, also: "me"}
b:
  also: "me"

Merge arrays

Given a sample.yml file of:

a:
  - 1
  - 2
  - 3
b:
  - 3
  - 4
  - 5

then

yq eval '. * {"a":.b}' sample.yml

will output

a:
  - 3
  - 4
  - 5
b:
  - 3
  - 4
  - 5

Merge, only existing fields

Given a sample.yml file of:

a:
  thing: one
  cat: frog
b:
  missing: two
  thing: two

then

yq eval '.a *? .b' sample.yml

will output

thing: two
cat: frog

Merge, appending arrays

Given a sample.yml file of:

a:
  array:
    - 1
    - 2
    - animal: dog
  value: coconut
b:
  array:
    - 3
    - 4
    - animal: cat
  value: banana

then

yq eval '.a *+ .b' sample.yml

will output

array:
  - 1
  - 2
  - animal: dog
  - 3
  - 4
  - animal: cat
value: banana

Merge, only existing fields, appending arrays

Given a sample.yml file of:

a:
  thing:
    - 1
    - 2
b:
  thing:
    - 3
    - 4
  another:
    - 1

then

yq eval '.a *?+ .b' sample.yml

will output

thing:
  - 1
  - 2
  - 3
  - 4

Merge, deeply merging arrays

Merging arrays deeply means arrays are merge like objects, with indexes as their key. In this case, we merge the first item in the array, and do nothing with the second.

Given a sample.yml file of:

a:
  - name: fred
    age: 12
  - name: bob
    age: 32
b:
  - name: fred
    age: 34

then

yq eval '.a *d .b' sample.yml

will output

- name: fred
  age: 34
- name: bob
  age: 32

Merge arrays of objects together, matching on a key

The approach, at a high level, is to reduce into a merged map (keyed by the unique key) and then convert that back into an array.

First the expression will create a map from the arrays keyed by '.a', the unique field we want to merge by. The reduce operator is merging '({}; . * $item )', so array elements with the matching key will be merged together.

Next, we convert the map back to an array, using reduce again, concatenating all the map values together.

Finally, we set the result of the merged array back into the first doc.

To use this, you will need to update '.myArray' in the expression to your array (e.g. .my.array), and '.a' to be the key field of your array (e.g. '.name')

Thanks Kev from stackoverflow

Given a sample.yml file of:

myArray:
  - a: apple
    b: appleB
  - a: kiwi
    b: kiwiB
  - a: banana
    b: bananaB
something: else

And another sample another.yml file of:

myArray:
  - a: banana
    c: bananaC
  - a: apple
    b: appleB2
  - a: dingo
    c: dingoC

then

yq eval-all '
(
  ((.myArray[] | {.a: .}) as $item ireduce ({}; . * $item )) as $uniqueMap
  | ( $uniqueMap  | to_entries | .[]) as $item ireduce([]; . + $item.value)
) as $mergedArray
| select(fi == 0) | .myArray = $mergedArray
' sample.yml another.yml

will output

myArray:
  - a: apple
    b: appleB2
  - a: kiwi
    b: kiwiB
  - a: banana
    b: bananaB
    c: bananaC
  - a: dingo
    c: dingoC
something: else

Merge to prefix an element

Given a sample.yml file of:

a: cat
b: dog

then

yq eval '. * {"a": {"c": .a}}' sample.yml

will output

a:
  c: cat
b: dog

Merge with simple aliases

Given a sample.yml file of:

a: &cat
  c: frog
b:
  f: *cat
c:
  g: thongs

then

yq eval '.c * .b' sample.yml

will output

g: thongs
f: *cat

Merge copies anchor names

Given a sample.yml file of:

a:
  c: &cat frog
b:
  f: *cat
c:
  g: thongs

then

yq eval '.c * .a' sample.yml

will output

g: thongs
c: &cat frog

Merge with merge anchors

Given a sample.yml file of:

foo: &foo
  a: foo_a
  thing: foo_thing
  c: foo_c
bar: &bar
  b: bar_b
  thing: bar_thing
  c: bar_c
foobarList:
  b: foobarList_b
  !!merge <<:
    - *foo
    - *bar
  c: foobarList_c
foobar:
  c: foobar_c
  !!merge <<: *foo
  thing: foobar_thing

then

yq eval '.foobar * .foobarList' sample.yml

will output

c: foobarList_c
!!merge <<:
  - *foo
  - *bar
thing: foobar_thing
b: foobarList_b