jorgecarleitao commented on pull request #68:
URL: https://github.com/apache/arrow-datafusion/pull/68#issuecomment-913998272


   @houqp , the argument `groups_filter: Arc<dyn Fn(usize, &RowGroupMetaData) 
-> bool>` of the `Reader` is used to filter row groups; the first argument is 
the row group, the second is its metadata, which includes all statistics.
   
   In more recent versions we also have `Arc<dyn Fn(&PageHeader) -> bool>` to 
skip individual pages based on their statistics.
   
   I am not familiar with this code-base, but I would expect that we create 
such mapping out of expressions: every row group is selected or not based on 
its metadata with statistics, and potentially its number in the parquet file 
for partitioned reads of a single file.


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