Jo is ds/mapseq-reader the correct thing to use when I for example want to provide data for #clerk ? (I have a dataset and I like a seq of maps). Yea ok I figure the dosctring literally says my description 😅

How can I perform an aggregation like

SELECT
    category,
    stragg(id, ', ') AS ids
FROM table
GROUP BY category

(ds/->dataset [{"id" 1, "name" "bob"} {"id" 2, "name" "bob"}, {"id" 3, "name" "alice"}])
|  name | id |
|-------|---:|
|   bob |  1 |
|   bob |  2 |
| alice |  3 |

| name  | ids  |
|-------+------|
| bob   | 1, 2 |
| alice | 3    |

tc/fold-by is your friend here:

(-> (tc/dataset [{"id" 1, "name" "bob"} {"id" 2, "name" "bob"}, {"id" 3, "name" "alice"}])
    (tc/fold-by ["name"] (partial str/join ", ")))

;; => _unnamed [2 2]:
;;    |  name |   id |
;;    |-------|------|
;;    |   bob | 1, 2 |
;;    | alice |    3 |

And the https://techascent.github.io/tech.ml.dataset/tech.v3.dataset.reductions.html#var-reducer for larger datasets that avoids construction of the intermediate column values:

tech.v3.dataset.reductions-test> (ds-reduce/group-by-column-agg 
                                  "name"
                                  {"id" (ds-reduce/reducer 
                                         "id" 
                                         (fn [ctx val]
                                           (let [first? (nil? ctx)
                                                 ^StringBuilder ctx (or ctx (StringBuilder.))]
                                             (when-not first? (.append ctx ", "))
                                             (.append ctx val)))
                                         #(.toString ^Object %))}
                                  [ds])
                                                           
                                                                
name-aggregation [2 2]:

|  name |   id |
|-------|------|
|   bob | 1, 2 |
| alice |    3 |