[GitHub] [arrow-rs] HaoYang670 opened a new issue #1511: Speed up the `substring` kernel

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

HaoYang670 opened a new issue #1511:
URL: https://github.com/apache/arrow-rs/issues/1511


   **Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
   https://github.com/apache/arrow-rs/blob/master/arrow/src/compute/kernels/substring.rs#L44
   ```rust
       let mut new_values = MutableBuffer::new(0); // we have no way to estimate how much this will be.
   ```
   We can estimate the memory we need by firstly calculating the length of each substring. This can improve the performance because we don't need to reallocate memory when building buffer.
   


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