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Posted to github@arrow.apache.org by "Rich-T-kid (via GitHub)" <gi...@apache.org> on 2026/08/15 02:37:30 UTC
[PR] implement retain on metadata [arrow-rs]
Rich-T-kid opened a new pull request, #10695:
URL: https://github.com/apache/arrow-rs/pull/10695
# Which issue does this PR close?
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- Closes #10683.
# Rationale for this change
see #10683
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# What changes are included in this PR?
implements `retain` on metadata. The underlying BTreeMap is allocation free unless the `Arc` pointer is shared
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# Are these changes tested?
yes
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# Are there any user-facing changes?
yes, new `retain` method on the metadata struct
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Re: [PR] implement `Metadata::retain` [arrow-rs]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb merged PR #10695:
URL: https://github.com/apache/arrow-rs/pull/10695
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Re: [PR] implement retain on metadata [arrow-rs]
Posted by "Rich-T-kid (via GitHub)" <gi...@apache.org>.
Rich-T-kid commented on code in PR #10695:
URL: https://github.com/apache/arrow-rs/pull/10695#discussion_r3789599853
##########
arrow-schema/src/metadata.rs:
##########
@@ -146,6 +146,19 @@ impl Metadata {
pub fn values(&self) -> impl Iterator<Item = &String> {
self.iter().map(|(_, value)| value)
}
+
+ /// Retains only the entries for which `f(&key, &mut value)` returns `true`.
+ ///
+ /// Entries for which `f` returns `false` are removed. Retained entries
+ /// remain in their original (sorted) order.
+ ///
+ /// Clones the underlying map if (and only if) it is shared.
+ pub fn retain<F>(&mut self, eq: F)
+ where
+ F: FnMut(&String, &mut String) -> bool,
+ {
+ Arc::make_mut(self.0.get_or_insert_default()).retain(eq);
Review Comment:
ah good catch!
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Re: [PR] implement retain on metadata [arrow-rs]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on code in PR #10695:
URL: https://github.com/apache/arrow-rs/pull/10695#discussion_r3789217137
##########
arrow-schema/src/metadata.rs:
##########
@@ -146,6 +146,19 @@ impl Metadata {
pub fn values(&self) -> impl Iterator<Item = &String> {
self.iter().map(|(_, value)| value)
}
+
+ /// Retains only the entries for which `f(&key, &mut value)` returns `true`.
+ ///
+ /// Entries for which `f` returns `false` are removed. Retained entries
+ /// remain in their original (sorted) order.
+ ///
+ /// Clones the underlying map if (and only if) it is shared.
+ pub fn retain<F>(&mut self, eq: F)
+ where
+ F: FnMut(&String, &mut String) -> bool,
+ {
+ Arc::make_mut(self.0.get_or_insert_default()).retain(eq);
Review Comment:
Does calling get_or_insert_default mean this method would turn a metadata that had a None inner map into aSome(empty map)?
I think it would make more sense to do nothing if `self.0` is None
##########
arrow-schema/src/metadata.rs:
##########
@@ -445,6 +458,35 @@ mod tests {
assert_eq!(format!("{metadata:?}"), r#"{"a": "1", "b": "2"}"#);
assert_eq!(format!("{:?}", Metadata::new()), "{}");
}
+ #[test]
+ fn test_retain() {
+ let mut metadata =
+ Metadata::from([("a", "1"), ("b", "2"), ("c", "3"), ("d", "4"), ("e", "5")]);
+
+ metadata.retain(|k, _| -> bool { k >= &String::from("c") });
+
+ let result_map = Metadata::from([("c", "3"), ("d", "4"), ("e", "5")]);
+ assert_eq!(metadata, result_map)
+ }
+
+ #[test]
Review Comment:
Can you please add a test that shows what happens when retain is called on a empty Metadata (`None`)? It should I think still be `None`
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Re: [PR] implement retain on metadata [arrow-rs]
Posted by "Rich-T-kid (via GitHub)" <gi...@apache.org>.
Rich-T-kid commented on code in PR #10695:
URL: https://github.com/apache/arrow-rs/pull/10695#discussion_r3789604765
##########
arrow-schema/src/metadata.rs:
##########
@@ -445,6 +458,35 @@ mod tests {
assert_eq!(format!("{metadata:?}"), r#"{"a": "1", "b": "2"}"#);
assert_eq!(format!("{:?}", Metadata::new()), "{}");
}
+ #[test]
+ fn test_retain() {
+ let mut metadata =
+ Metadata::from([("a", "1"), ("b", "2"), ("c", "3"), ("d", "4"), ("e", "5")]);
+
+ metadata.retain(|k, _| -> bool { k >= &String::from("c") });
+
+ let result_map = Metadata::from([("c", "3"), ("d", "4"), ("e", "5")]);
+ assert_eq!(metadata, result_map)
+ }
+
+ #[test]
Review Comment:
also added a test for when `retain()` clears all the maps contents. the metadata becomes `None`
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