alamb commented on a change in pull request #923:
URL: https://github.com/apache/arrow-rs/pull/923#discussion_r745032837
##########
File path: arrow/src/datatypes/field.rs
##########
@@ -107,6 +107,47 @@ impl Field {
self.nullable
}
+ /// Returns a (flattened) vector containing all fields contained within
this field (including it self)
+ pub(crate) fn fields(&self) -> Vec<&Field> {
+ let mut collected_fields = vec![self];
+ match &self.data_type {
+ DataType::Struct(fields) | DataType::Union(fields) =>
collected_fields
+ .append(&mut fields.iter().map(|f|
f.fields()).flatten().collect()),
Review comment:
I think you can save an intermediate `collect` here by doing something
like:
```suggestion
DataType::Struct(fields) | DataType::Union(fields) =>
collected_fields
.extend(fields.iter().map(|f| f.fields()).flatten()),
```
Probably doesn't make any practical difference, mostly a stylistic difference
##########
File path: arrow/src/datatypes/field.rs
##########
@@ -107,6 +107,47 @@ impl Field {
self.nullable
}
+ /// Returns a (flattened) vector containing all fields contained within
this field (including it self)
+ pub(crate) fn fields(&self) -> Vec<&Field> {
+ let mut collected_fields = vec![self];
+ match &self.data_type {
+ DataType::Struct(fields) | DataType::Union(fields) =>
collected_fields
+ .append(&mut fields.iter().map(|f|
f.fields()).flatten().collect()),
+ DataType::List(field)
+ | DataType::LargeList(field)
+ | DataType::FixedSizeList(field, _)
+ | DataType::Map(field, _) => collected_fields.push(field),
+ _ => (),
+ }
+
+ collected_fields
+ }
+
+ /// Adds all (potentially nested) `Field` instances selected by the
dictionary ID they use into
+ /// the `dictfields` vector.
+ fn collect_fields_with_dict_id<'a>(
+ &'a self,
+ dictfields: &'_ mut Vec<&'a Field>,
+ id: i64,
+ ) {
+ for field in self.fields() {
+ if let DataType::Dictionary(_, _) = field.data_type() {
+ if field.dict_id == id {
+ dictfields.push(field);
+ }
+ }
+ }
+ }
+
+ /// Returns a vector containing all (potentially nested) `Field` instances
selected by the
+ /// dictionary ID they use
+ #[inline]
+ pub(crate) fn fields_with_dict_id(&self, id: i64) -> Vec<&Field> {
+ let mut fields = Vec::new();
+ self.collect_fields_with_dict_id(&mut fields, id);
+ fields
+ }
Review comment:
If you are into the Rust style of functional programming, I think you
can avoid the use of `mut` and intermediate `Vec`s by using
https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.filter_map
Something like
```suggestion
/// Returns a vector containing all (potentially nested) `Field`
instances selected by the
/// dictionary ID they use
#[inline]
pub(crate) fn fields_with_dict_id(&self, id: i64) -> Vec<&Field> {
self.fields()
.into_iter()
.filter_map(|field| {
match field.data_type() {
DataType::Dictionary(_, _) if field.dict_id == id => {
Some(field)
}
_ => None
}
})
.collect()
}
```
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