Dandandan opened a new issue #717:
URL: https://github.com/apache/arrow-datafusion/issues/717


   **Is your feature request related to a problem or challenge? Please describe 
what you are trying to do.**
   While looking at adding support for more statistics on the Delta Lake 
`TableProvider` implementation I bumped into some limitation in our statistics 
API.
   
   Currently columnstatistics is a `Option<Vec<ColumnStatistics>>`.
   
   
https://github.com/apache/arrow-datafusion/blob/master/datafusion/src/datasource/datasource.rs#L37
   
   So, it should return the statistics by (correct) index regardless of the 
order in the files. 
   
   **Describe the solution you'd like**
   Either:
   * Return a `HashMap<String, ColumnStatistics>` rather than a 
`Option<Vec<ColumnStatistics>>`
   * Pass a `Schema` parameter to `TableProvider::statisitics` so the position 
can be found out.
   
   FWIW, Delta Lake / delta-rs takes the first approach and seems 
straightforward to implement and use.
   
   **Describe alternatives you've considered**
   
   **Additional context**
   


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