I just found a nice/weird/strange/unexpected side effect which actually gives me intended behavior, but looks so hacky :

{
  "type": "extraction",
  "dimension": "dim",
  "outputName": "display_dim",
  "extractionFn": {
    "type": "cascade",
    "extractionFns": [
      {
        "type": "registeredLookup",
        "lookup": "dim_display"
      }
    ]
  }
}

if you do a

topN

it will group them on the lookup key. However:

{
  "type": "extraction",
  "dimension": "dim",
  "outputName": "display_dim",
  "extractionFn": {
    "type": "cascade",
    "extractionFns": [
      {
        "type": "registeredLookup",
        "lookup": "dim_display"
      },
      {
        "type": "javascript",
        "function": "function(value) { return value; }"
      }
    ]
  }
}

will actually group by the lookup value i.e. merge rows as long as the lookup values are the same, which is intended in my use case. Is there any cleaner way to get this behavior, because leaving it like this needs a lot of comments to make the next dev understand, why it looks this way.

Is

"injective":true

in the lookup definition? If so, this seems like the intended behavior, as the values will only materialize after aggregation. However, if injective is false, then I wouldn't expect that behavior.

I didn’t know about this property, but our lookup generator supports it and yep, it’s misconfigured. tnx