alamb commented on code in PR #7919:
URL: https://github.com/apache/arrow-rs/pull/7919#discussion_r2211278693
##########
parquet-variant/src/variant.rs:
##########
@@ -1063,6 +1064,17 @@ impl<'m, 'v> Variant<'m, 'v> {
_ => None,
}
}
+
+ /// Return a new Variant with the path followed.
+ ///
+ /// If the path is not found, `None` is returned.
+ pub fn get_path(&self, path: &VariantPath) -> Option<Variant> {
Review Comment:
👍
##########
parquet-variant-compute/src/variant_get.rs:
##########
@@ -0,0 +1,202 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+use std::sync::Arc;
+
+use arrow::{
+ array::{Array, ArrayRef},
+ compute::CastOptions,
+ error::Result,
+};
+use arrow_schema::{ArrowError, Field};
+use parquet_variant::path::VariantPath;
+
+use crate::{VariantArray, VariantArrayBuilder};
+
+/// Returns an array with the specified path extracted from the variant values.
+///
+/// The return array type depends on the `as_type` field of the options
parameter
+/// 1. `as_type: None`: a VariantArray is returned. The values in this new
VariantArray will point
+/// to the specified path.
+/// 2. `as_type: Some(<specific field>)`: an array of the specified type is
returned.
+pub fn variant_get(input: &ArrayRef, options: GetOptions) -> Result<ArrayRef> {
+ let variant_array: &VariantArray =
input.as_any().downcast_ref().ok_or_else(|| {
+ ArrowError::InvalidArgumentError(
+ "expected a VariantArray as the input for variant_get".to_owned(),
+ )
+ })?;
+
+ if let Some(as_type) = options.as_type {
+ return Err(ArrowError::NotYetImplemented(format!(
+ "getting a {} from a VariantArray is not implemented yet",
+ as_type
+ )));
+ }
+
+ let mut builder = VariantArrayBuilder::new(variant_array.len());
+ for i in 0..variant_array.len() {
+ let new_variant = variant_array.value(i);
Review Comment:
> For efficiency reasons we should strongly consider some kind of direct
pathing support in VariantArray itself. Otherwise, it would be far too easy for
a caller to accidentally do quadratic work when repeatedly calling
value+get_path pairs for different paths.
I think @scovich is saying that the variant_get kernel (on `VariantArray`
should have a special case that knows how to look for a shredded sub field --
and if for example it is asking for `a` and the the `typed_value.a` column
exists, variant_get could simply return that `a` column (already as an arrow
array, no actual Variant manipulation required)
- I filed https://github.com/apache/arrow-rs/issues/7941 to track this
##########
parquet-variant/src/path.rs:
##########
@@ -0,0 +1,64 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+use std::{borrow::Cow, ops::Deref};
+
+/// Represents a qualified path to a potential subfield or index of a variant
value.
+#[derive(Debug, Clone)]
+pub struct VariantPath<'a>(Vec<VariantPathElement<'a>>);
+
+impl<'a> VariantPath<'a> {
+ pub fn new(path: Vec<VariantPathElement<'a>>) -> Self {
+ Self(path)
+ }
+
+ pub fn path(&self) -> &Vec<VariantPathElement> {
+ &self.0
+ }
+}
+
+impl<'a> From<Vec<VariantPathElement<'a>>> for VariantPath<'a> {
+ fn from(value: Vec<VariantPathElement<'a>>) -> Self {
+ Self::new(value)
+ }
+}
+
+impl<'a> Deref for VariantPath<'a> {
+ type Target = [VariantPathElement<'a>];
+
+ fn deref(&self) -> &Self::Target {
+ &self.0
+ }
+}
+
+/// Element of a path
Review Comment:
this is lovely
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