How to join two list into one on some common fields?

Question

I want to join two list into one using deep copy.
E.g.

list1:
[
   {"key1":["val1"]}, 
   {"key2":["val2", "val3"]}
]

list2:
[
   {"key2":["val2", "val4"]},
   {"key3":["val5"]}
]

I want the output to be :
[
   {"key1":["val1"]}, 
   {"key2":["val2", "val3", "val4"]}
   {"key3":["val5"]}
]

I tried std.mergePatch but it just overrides the previous list. Thanks,

Answer 1

Copying below a possible solution, which "unrolls" the list(s) down to single key-value entries, then aggregate them into the manifested object, note that the code is long because of detailed comments.

local list1 = [
  { key1: ['val1'] },
  { key2: ['val2', 'val3'] },
];

local list2 = [
  { key2: ['val2', 'val4'] },
  { key3: ['val5'] },
];

// Hash key for the `seen` dictionary
local hash(kv) = std.md5(std.toString(kv));

// Loop over the passed array of objs, aggregating each final/"leaf" KV pair,
// but only if not seen before
local mergeLists(lists) = std.foldl(
  function(mergedObj, kv) mergedObj {
    ret+: if (hash(kv) in mergedObj.seen) then {} else {
      [kv.key]+: [kv.value],
    },
    seen+:: {
      [hash(kv)]: true,
    },
  },
  // "Unroll" the (sum of) list(s), we need 3 loops:
  // 1) main list
  // 2) each entry's object from 1)
  // 3) each "final" list of values
  // -> convert them into single Key-Value (mini) objects
  [
    { key: k, value: v }
    for list in lists
    for k in std.objectFields(list)
    for v in list[k]
  ],
  { seen:: {} },
);

mergeLists(list1 + list2).ret