ydb/yql/essentials/tests/s-expressions/suites/SingleYamrOperation/LengthOfTableInsideMap.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 x (Read! world mr_source (Key '('table (String 'Input2))) '('key 'subkey 'value) '()))
(let world (Left! x))
(let table2 (Right! x))
(let table3 (Map table1 (lambda '(item) (block '(
    (let s (AsStruct 
       '('key (Member item 'key))
       '('subkey (ToString (Length table2)))
       '('value (Member item 'value))
    ))
    
    (return s)
)))))

(let mr_sink (DataSink 'yt (quote plato)))
(let world (Write! world mr_sink (Key '('table (String 'Output))) table3 '('('mode 'append))))
(let world (Commit! world mr_sink))
(return world)
)