unique.cue

import "list"

a: [{id: 1}, {id: 2}]
b: [{id: 1}, {id: 1}]
c: [{id: 1}, {id: 2}, {id: 2}]

a_ids:: [x.id for x in a]
a_unique: list.UniqueItems(a_ids)

unique :: {
  input : _
  output : list.UniqueItems([x.id for x in input])
}

b_unique : (unique & {input: b}).output
c_unique : (unique & {input: c}).output

unique2.cue

import "list"

a: [{id: 1}, {id: 2}]
b: [{id: 1}, {id: 2}, {id: 2}]

func1:: {input: _, output: _}
unique_by:: {
  f: func1
  input: _
  output: list.UniqueItems([(f & {input: x}).output for x in input])
}

get_id:: func1 & {
  input: _
  output: input.id
}

a_unique : (unique_by & {input: a, f: get_id}).output
b_unique : (unique_by & {input: b, f: get_id}).output