rust - How do I avoid unwrap when converting a vector of Options or Results to only the successful values?

Question

I have a Vec<Result<T, E>> and I want to ignore all Err values, converting it into a Vec<T>. I can do this:

vec.into_iter().filter(|e| e.is_ok()).map(|e| e.unwrap()).collect()

This is safe, but I want to avoid using unwrap. Is there a better way to write this?

Answer 1

I want to ignore all Err values

Since Result implements IntoIterator, you can convert your Vec into an iterator (which will be an iterator of iterators) and then flatten it:

• Iterator::flatten:

  vec.into_iter().flatten().collect()
  

• Iterator::flat_map:

  vec.into_iter().flat_map(|e| e).collect()
  

These methods also work for Option, which also implements IntoIterator.

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You could also convert the Result into an Option and use Iterator::filter_map:

vec.into_iter().filter_map(|e| e.ok()).collect()