ydb/yql/essentials/tests/s-expressions/suites/ManyYamrOperations/MapThenExtend.yql

(
#comment
(let mr_source (DataSource 'yt 'plato))
(let x (Read! world mr_source (Key '('table (String 'Input))) '('key 'subkey 'value) '()))
(let world (Left! x))
(let table1 (Right! x))
(let table1map (Map table1 (lambda '(item) (block '(
   (let s (Struct))
   (let s (AddMember s 'key (Member item 'key)))
   (let s (AddMember s 'subkey (String  '1)))
   (let s (AddMember s 'value (String 'v)))
   (return s)
)))))
(let mr_sink (DataSink 'yt 'plato))
(let world (Write! world mr_sink (Key '('table (String 'Output))) (Extend table1map table1map) '()))
(let world (Commit! world mr_sink))
(return world)
)