[GitHub] [arrow-rs] jorgecarleitao commented on pull request #389: make slice work for nested types

[GitBox <gi...@apache.org>]

jorgecarleitao commented on pull request #389:
URL: https://github.com/apache/arrow-rs/pull/389#issuecomment-855365462


   Isn't it possible to not offset the child data, and instead only offset the `offsets`, or do we have some logic around that assumes that offsets always start from 0?
   
   In arrow2, I am doing 
   
   ```
   impl<O: Offset> ListArray<O> {
       pub fn slice(&self, offset: usize, length: usize) -> Self {
           let validity = self.validity.clone().map(|x| x.slice(offset, length));
           let offsets = self.offsets.clone().slice(offset, length + 1);
           Self {
               data_type: self.data_type.clone(),
               offsets,
               values: self.values.clone(),
               validity,
               offset: self.offset + offset,
           }
       }
   }
   ```
   
   note how the `offsets` are sliced and the values are cloned. The `ListArray<O>::offset` is only used for compatibility with the C data interface.
   


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