no error when grouping by [column] not in dataset

[orbit-stabilizer]

Currently, we have the following, which is correct:

(-> (tc/dataset {:a []})
    (tc/group-by :b)
;; (err) Column not found: :b

However, when we run the following, we get an empty dataset and not an error:

(-> (tc/dataset {:a []})
    (tc/group-by [:b])
;; _unnamed [0 0]

Using group-by in this way should also return an error.

[cnuernber]

Great bug report and we agree this is the desired behavior!

tablecloth is built on TMD and we it appears in these situations TMD has reasonable responses thus far:

tech.v3.dataset-test> (ds/group-by->indexes (ds/empty-dataset) :a)
                       
{}
tech.v3.dataset-test> (ds/group-by-column->indexes (ds/empty-dataset) :a)
                       
Execution error at tech.v3.dataset.impl.dataset.Dataset/column (dataset.clj:308).
Column not found: :a
tech.v3.dataset-test> (ds/group-by-column->indexes (ds/->dataset {:a []}) :a)
                       
{}

Potentially the last case - {:a []} should return {:a (ds/empty-dataset)}.