szehon-ho edited a comment on issue #2783:
URL: https://github.com/apache/iceberg/issues/2783#issuecomment-873875087


   Preliminary analysis:  The BaseFile class uses some pruning logic, keeping a 
mapping called 'fromProjectionPos' that maps indexes in a projection (a subset 
of its columns) to real indexes in its column list.
   
   Ie, if the projected array has three elements which are fields 1,2, and 10 
of the original schema respectively, fromProjectionPos becomes {1, 2, 10}.
   
   This is usually fine but the Spark generated code in Spark 3 uses the 
original index to get all the fields (It's entry point is StructInternalRow: 
https://github.com/apache/iceberg/blob/master/spark/src/main/java/org/apache/iceberg/spark/source/StructInternalRow.java#L124.
 (here 'struct' is the BaseDataFile with the pruning mapping).  
   
   It calls getInt(0) expecting an int as per the real column at index 0, but 
due to the mapping we return value at index 1 which is actually a string and 
hence the error.


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