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  1. Apache Arrow
  2. ARROW-11799

[Rust] String and Binary arrays created with incorrect length from unbound iterator

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Details

    • Improvement
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • 3.0.0
    • 4.0.0
    • Rust

    Description

      While looking for a way to make loading array data from parquet files faster, I stumbled on an edge case where string and binary arrays are created with an incorrect length from an iterator with no upper bound.

      Here is a simple example:

      ```
       // iterator that doesn't declare (upper) size bound
              let string_iter = (0..).scan(0usize, |pos, i| { 
                  if *pos < 10 {
                      *pos += 1;
                      Some(Some(format!("value {}", i)))
                  }
                  else 

      {                 // actually returns up to 10 values                 None             }

              })
              // limited using take()
              .take(100);

              let (lower_size_bound, upper_size_bound) = string_iter.size_hint();
              assert_eq!(lower_size_bound, 0);
              // the upper bound, defined by take above, is 100
              assert_eq!(upper_size_bound, Some(100));
              let string_array: StringArray = string_iter.collect();
              // but the actual number of items in the array is 10
              assert_eq!(string_array.len(), 10);
      ```

      Fortunately this is easy to fix by using the length of the child offset array and I will be creating a PR for this shortly.

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              yordan-pavlov Yordan Pavlov
              yordan-pavlov Yordan Pavlov
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