alamb commented on a change in pull request #1088:
URL: https://github.com/apache/arrow-datafusion/pull/1088#discussion_r725472806
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File path: datafusion/src/optimizer/projection_push_down.rs
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@@ -417,9 +416,15 @@ fn optimize_plan(
})
.collect::<Result<Vec<_>>>()?;
+ let mut new_schema = Vec::new();
+ for df_field in schema.fields() {
+ if union_required_fields.contains(df_field.field()) {
+ new_schema.push(df_field.clone());
+ }
+ }
Review comment:
Yeah it took me a while to become comfortable with the functional style.
As an aside - I also later realized that using this functional style is more
than just about code structure / readability -- it is one of the key ways Rust
does fast and safe: in the `mut Vec<..>` version, every time data is pushed the
capacity of the vec needs to be checked and extended if not large enough. In
the `iter()` version often the Vec can be created up front and then written
directly into.
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