alamb commented on code in PR #4675: URL: https://github.com/apache/arrow-datafusion/pull/4675#discussion_r1054883972
########## datafusion/physical-expr/src/aggregate/moving_min_max.rs: ########## @@ -0,0 +1,330 @@ +// 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. + +// The implementation is taken from https://github.com/spebern/moving_min_max/blob/master/src/lib.rs. Review Comment: 👍 ########## datafusion/physical-expr/src/aggregate/mod.rs: ########## @@ -101,4 +102,12 @@ pub trait AggregateExpr: Send + Sync + Debug { self ))) } + + /// Creates accumulator implementation that supports retract Review Comment: 👍 Perfect ########## datafusion/core/src/datasource/mod.rs: ########## @@ -155,11 +155,14 @@ pub async fn get_statistics_with_limit( fn create_max_min_accs( schema: &Schema, -) -> (Vec<Option<MaxAccumulator>>, Vec<Option<MinAccumulator>>) { - let max_values: Vec<Option<MaxAccumulator>> = schema +) -> ( Review Comment: Likewise the change in this file does not make sense to me -- why is a sliding accumulator needed (only) for calculating minimums? ########## datafusion/physical-expr/src/aggregate/moving_min_max.rs: ########## @@ -0,0 +1,330 @@ +// 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. + +// The implementation is taken from https://github.com/spebern/moving_min_max/blob/master/src/lib.rs. + +//! Keep track of the minimum or maximum value in a sliding window. +//! +//! `moving min max` provides one data structure for keeping track of the +//! minimum value and one for keeping track of the maximum value in a sliding +//! window. +//! +//! Each element is stored with the current min/max. One stack to push and another one for pop. If pop stack is empty, +//! push to this stack all elements popped from first stack while updating their current min/max. Now pop from +//! the second stack (MovingMin/Max struct works as a queue). To find the minimum element of the queue, +//! look at the smallest/largest two elements of the individual stacks, then take the minimum of those two values. +//! +//! The complexity of the operations are +//! - O(1) for getting the minimum/maximum +//! - O(1) for push +//! - amortized O(1) for pop + +/// let mut moving_min = MovingMin::<i32>::new(); +/// moving_min.push(2); +/// moving_min.push(1); +/// moving_min.push(3); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(2)); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(1)); +/// +/// assert_eq!(moving_min.min(), Some(&3)); +/// assert_eq!(moving_min.pop(), Some(3)); +/// +/// assert_eq!(moving_min.min(), None); +/// assert_eq!(moving_min.pop(), None); +#[derive(Debug)] +pub struct MovingMin<T> { + push_stack: Vec<(T, T)>, + pop_stack: Vec<(T, T)>, +} + +impl<T: Clone + PartialOrd> Default for MovingMin<T> { + fn default() -> Self { + Self { + push_stack: Vec::new(), + pop_stack: Vec::new(), + } + } +} + +impl<T: Clone + PartialOrd> MovingMin<T> { + /// Creates a new `MovingMin` to keep track of the minimum in a sliding + /// window. + #[inline] + pub fn new() -> Self { + Self::default() + } + + /// Creates a new `MovingMin` to keep track of the minimum in a sliding + /// window with `capacity` allocated slots. + #[inline] + pub fn with_capacity(capacity: usize) -> Self { + Self { + push_stack: Vec::with_capacity(capacity), + pop_stack: Vec::with_capacity(capacity), + } + } + + /// Returns the minimum of the sliding window or `None` if the window is + /// empty. + #[inline] + pub fn min(&self) -> Option<&T> { + match (self.push_stack.last(), self.pop_stack.last()) { + (None, None) => None, + (Some((_, min)), None) => Some(min), + (None, Some((_, min))) => Some(min), + (Some((_, a)), Some((_, b))) => Some(if a < b { a } else { b }), + } + } + + /// Pushes a new element into the sliding window. + #[inline] + pub fn push(&mut self, val: T) { + self.push_stack.push(match self.push_stack.last() { + Some((_, min)) => { + if val > *min { + (val, min.clone()) + } else { + (val.clone(), val) + } + } + None => (val.clone(), val), + }); + } + + /// Removes and returns the last value of the sliding window. + #[inline] + pub fn pop(&mut self) -> Option<T> { + if self.pop_stack.is_empty() { + match self.push_stack.pop() { + Some((val, _)) => { + let mut last = (val.clone(), val); + self.pop_stack.push(last.clone()); + while let Some((val, _)) = self.push_stack.pop() { + let min = if last.1 < val { + last.1.clone() + } else { + val.clone() + }; + last = (val.clone(), min); + self.pop_stack.push(last.clone()); + } + } + None => return None, + } + } + self.pop_stack.pop().map(|(val, _)| val) + } + + /// Returns the number of elements stored in the sliding window. + #[inline] + pub fn len(&self) -> usize { + self.push_stack.len() + self.pop_stack.len() + } + + /// Returns `true` if the moving window contains no elements. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } +} + +/// let mut moving_max = MovingMax::<i32>::new(); +/// moving_max.push(2); +/// moving_max.push(3); +/// moving_max.push(1); +/// +/// assert_eq!(moving_max.max(), Some(&3)); +/// assert_eq!(moving_max.pop(), Some(2)); +/// +/// assert_eq!(moving_max.max(), Some(&3)); +/// assert_eq!(moving_max.pop(), Some(3)); +/// +/// assert_eq!(moving_max.max(), Some(&1)); +/// assert_eq!(moving_max.pop(), Some(1)); +/// +/// assert_eq!(moving_max.max(), None); +/// assert_eq!(moving_max.pop(), None); +#[derive(Debug)] +pub struct MovingMax<T> { + push_stack: Vec<(T, T)>, + pop_stack: Vec<(T, T)>, +} + +impl<T: Clone + PartialOrd> Default for MovingMax<T> { + fn default() -> Self { + Self { + push_stack: Vec::new(), + pop_stack: Vec::new(), + } + } +} + +impl<T: Clone + PartialOrd> MovingMax<T> { + /// Creates a new `MovingMax` to keep track of the maximum in a sliding window. + #[inline] + pub fn new() -> Self { + Self::default() + } + + /// Creates a new `MovingMax` to keep track of the maximum in a sliding window with + /// `capacity` allocated slots. + #[inline] + pub fn with_capacity(capacity: usize) -> Self { + Self { + push_stack: Vec::with_capacity(capacity), + pop_stack: Vec::with_capacity(capacity), + } + } + + /// Returns the maximum of the sliding window or `None` if the window is empty. + #[inline] + pub fn max(&self) -> Option<&T> { + match (self.push_stack.last(), self.pop_stack.last()) { + (None, None) => None, + (Some((_, max)), None) => Some(max), + (None, Some((_, max))) => Some(max), + (Some((_, a)), Some((_, b))) => Some(if a > b { a } else { b }), + } + } + + /// Pushes a new element into the sliding window. + #[inline] + pub fn push(&mut self, val: T) { + self.push_stack.push(match self.push_stack.last() { + Some((_, max)) => { + if val < *max { + (val, max.clone()) + } else { + (val.clone(), val) + } + } + None => (val.clone(), val), + }); + } + + /// Removes and returns the last value of the sliding window. + #[inline] + pub fn pop(&mut self) -> Option<T> { + if self.pop_stack.is_empty() { + match self.push_stack.pop() { + Some((val, _)) => { + let mut last = (val.clone(), val); + self.pop_stack.push(last.clone()); + while let Some((val, _)) = self.push_stack.pop() { + let max = if last.1 > val { + last.1.clone() + } else { + val.clone() + }; + last = (val.clone(), max); + self.pop_stack.push(last.clone()); + } + } + None => return None, + } + } + self.pop_stack.pop().map(|(val, _)| val) + } + + /// Returns the number of elements stored in the sliding window. + #[inline] + pub fn len(&self) -> usize { + self.push_stack.len() + self.pop_stack.len() + } + + /// Returns `true` if the moving window contains no elements. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } +} + +#[cfg(test)] +mod tests { + use super::*; + use datafusion_common::Result; + use rand::Rng; + + fn get_random_vec_i32(len: usize) -> Vec<i32> { + let mut rng = rand::thread_rng(); + let mut input = Vec::with_capacity(len); + for _i in 0..len { + input.push(rng.gen_range(0..100)); + } + input + } + + fn moving_min_i32(len: usize, n_sliding_window: usize) -> Result<()> { + let data = get_random_vec_i32(len); + let mut expected = Vec::with_capacity(len); + let mut moving_min = MovingMin::<i32>::new(); + let mut res = Vec::with_capacity(len); + for i in 0..len { + let start = i.saturating_sub(n_sliding_window); + expected.push(*data[start..i + 1].iter().min().unwrap()); Review Comment: 👍 ########## datafusion/core/src/datasource/file_format/parquet.rs: ########## @@ -220,7 +220,7 @@ impl FileFormat for ParquetFormat { } fn summarize_min_max( - max_values: &mut [Option<MaxAccumulator>], + max_values: &mut [Option<SlidingMaxAccumulator>], Review Comment: I don't understand this change ########## datafusion/physical-expr/src/aggregate/min_max.rs: ########## @@ -703,6 +743,10 @@ impl AggregateExpr for Min { self.data_type.clone(), ))) } + + fn create_sliding_accumulator(&self) -> Result<Box<dyn Accumulator>> { Review Comment: 👍 ########## datafusion/physical-expr/src/aggregate/moving_min_max.rs: ########## @@ -0,0 +1,264 @@ +// 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. + +// The implementation is taken from https://github.com/spebern/moving_min_max/blob/master/src/lib.rs. + +//! Keep track of the minimum or maximum value in a sliding window. +//! +//! `moving min max` provides one data structure for keeping track of the +//! minimum value and one for keeping track of the maximum value in a sliding +//! window. +//! +//! Each element is stored with the current min/max. One stack to push and another one for pop. If pop stack is empty, +//! push to this stack all elements popped from first stack while updating their current min/max. Now pop from +//! the second stack (MovingMin/Max struct works as a queue). To find the minimum element of the queue, +//! look at the smallest/largest two elements of the individual stacks, then take the minimum of those two values. +//! +//! The complexity of the operations are +//! - O(1) for getting the minimum/maximum +//! - O(1) for push +//! - amortized O(1) for pop + +/// let mut moving_min = MovingMin::<i32>::new(); +/// moving_min.push(2); +/// moving_min.push(1); +/// moving_min.push(3); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(2)); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(1)); +/// +/// assert_eq!(moving_min.min(), Some(&3)); +/// assert_eq!(moving_min.pop(), Some(3)); +/// +/// assert_eq!(moving_min.min(), None); +/// assert_eq!(moving_min.pop(), None); Review Comment: These tests still aren't running -- if we are going to have example code I think they should be in backticks so they are part of the doctests (and tested via `cargo test`) ########## datafusion/physical-expr/src/aggregate/moving_min_max.rs: ########## @@ -0,0 +1,330 @@ +// 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. + +// The implementation is taken from https://github.com/spebern/moving_min_max/blob/master/src/lib.rs. + +//! Keep track of the minimum or maximum value in a sliding window. +//! +//! `moving min max` provides one data structure for keeping track of the +//! minimum value and one for keeping track of the maximum value in a sliding +//! window. +//! +//! Each element is stored with the current min/max. One stack to push and another one for pop. If pop stack is empty, +//! push to this stack all elements popped from first stack while updating their current min/max. Now pop from +//! the second stack (MovingMin/Max struct works as a queue). To find the minimum element of the queue, +//! look at the smallest/largest two elements of the individual stacks, then take the minimum of those two values. +//! +//! The complexity of the operations are +//! - O(1) for getting the minimum/maximum +//! - O(1) for push +//! - amortized O(1) for pop + +/// let mut moving_min = MovingMin::<i32>::new(); +/// moving_min.push(2); +/// moving_min.push(1); +/// moving_min.push(3); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(2)); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(1)); +/// +/// assert_eq!(moving_min.min(), Some(&3)); +/// assert_eq!(moving_min.pop(), Some(3)); +/// +/// assert_eq!(moving_min.min(), None); +/// assert_eq!(moving_min.pop(), None); +#[derive(Debug)] +pub struct MovingMin<T> { + push_stack: Vec<(T, T)>, + pop_stack: Vec<(T, T)>, +} + +impl<T: Clone + PartialOrd> Default for MovingMin<T> { + fn default() -> Self { + Self { + push_stack: Vec::new(), + pop_stack: Vec::new(), + } + } +} + +impl<T: Clone + PartialOrd> MovingMin<T> { + /// Creates a new `MovingMin` to keep track of the minimum in a sliding + /// window. + #[inline] + pub fn new() -> Self { + Self::default() + } + + /// Creates a new `MovingMin` to keep track of the minimum in a sliding + /// window with `capacity` allocated slots. + #[inline] + pub fn with_capacity(capacity: usize) -> Self { + Self { + push_stack: Vec::with_capacity(capacity), + pop_stack: Vec::with_capacity(capacity), + } + } + + /// Returns the minimum of the sliding window or `None` if the window is + /// empty. + #[inline] + pub fn min(&self) -> Option<&T> { + match (self.push_stack.last(), self.pop_stack.last()) { + (None, None) => None, + (Some((_, min)), None) => Some(min), + (None, Some((_, min))) => Some(min), + (Some((_, a)), Some((_, b))) => Some(if a < b { a } else { b }), + } + } + + /// Pushes a new element into the sliding window. + #[inline] + pub fn push(&mut self, val: T) { + self.push_stack.push(match self.push_stack.last() { + Some((_, min)) => { + if val > *min { + (val, min.clone()) + } else { + (val.clone(), val) + } + } + None => (val.clone(), val), + }); + } + + /// Removes and returns the last value of the sliding window. + #[inline] + pub fn pop(&mut self) -> Option<T> { + if self.pop_stack.is_empty() { + match self.push_stack.pop() { + Some((val, _)) => { + let mut last = (val.clone(), val); + self.pop_stack.push(last.clone()); + while let Some((val, _)) = self.push_stack.pop() { + let min = if last.1 < val { + last.1.clone() + } else { + val.clone() + }; + last = (val.clone(), min); + self.pop_stack.push(last.clone()); + } + } + None => return None, + } + } + self.pop_stack.pop().map(|(val, _)| val) + } + + /// Returns the number of elements stored in the sliding window. + #[inline] + pub fn len(&self) -> usize { + self.push_stack.len() + self.pop_stack.len() + } + + /// Returns `true` if the moving window contains no elements. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } +} + +/// let mut moving_max = MovingMax::<i32>::new(); +/// moving_max.push(2); +/// moving_max.push(3); +/// moving_max.push(1); +/// +/// assert_eq!(moving_max.max(), Some(&3)); +/// assert_eq!(moving_max.pop(), Some(2)); +/// +/// assert_eq!(moving_max.max(), Some(&3)); +/// assert_eq!(moving_max.pop(), Some(3)); +/// +/// assert_eq!(moving_max.max(), Some(&1)); +/// assert_eq!(moving_max.pop(), Some(1)); +/// +/// assert_eq!(moving_max.max(), None); +/// assert_eq!(moving_max.pop(), None); +#[derive(Debug)] +pub struct MovingMax<T> { + push_stack: Vec<(T, T)>, + pop_stack: Vec<(T, T)>, +} + +impl<T: Clone + PartialOrd> Default for MovingMax<T> { + fn default() -> Self { + Self { + push_stack: Vec::new(), + pop_stack: Vec::new(), + } + } +} + +impl<T: Clone + PartialOrd> MovingMax<T> { + /// Creates a new `MovingMax` to keep track of the maximum in a sliding window. + #[inline] + pub fn new() -> Self { + Self::default() + } + + /// Creates a new `MovingMax` to keep track of the maximum in a sliding window with + /// `capacity` allocated slots. + #[inline] + pub fn with_capacity(capacity: usize) -> Self { + Self { + push_stack: Vec::with_capacity(capacity), + pop_stack: Vec::with_capacity(capacity), + } + } + + /// Returns the maximum of the sliding window or `None` if the window is empty. + #[inline] + pub fn max(&self) -> Option<&T> { + match (self.push_stack.last(), self.pop_stack.last()) { + (None, None) => None, + (Some((_, max)), None) => Some(max), + (None, Some((_, max))) => Some(max), + (Some((_, a)), Some((_, b))) => Some(if a > b { a } else { b }), + } + } + + /// Pushes a new element into the sliding window. + #[inline] + pub fn push(&mut self, val: T) { + self.push_stack.push(match self.push_stack.last() { + Some((_, max)) => { + if val < *max { + (val, max.clone()) + } else { + (val.clone(), val) + } + } + None => (val.clone(), val), + }); + } + + /// Removes and returns the last value of the sliding window. + #[inline] + pub fn pop(&mut self) -> Option<T> { + if self.pop_stack.is_empty() { + match self.push_stack.pop() { + Some((val, _)) => { + let mut last = (val.clone(), val); + self.pop_stack.push(last.clone()); + while let Some((val, _)) = self.push_stack.pop() { + let max = if last.1 > val { + last.1.clone() + } else { + val.clone() + }; + last = (val.clone(), max); + self.pop_stack.push(last.clone()); + } + } + None => return None, + } + } + self.pop_stack.pop().map(|(val, _)| val) + } + + /// Returns the number of elements stored in the sliding window. + #[inline] + pub fn len(&self) -> usize { + self.push_stack.len() + self.pop_stack.len() + } + + /// Returns `true` if the moving window contains no elements. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } +} + +#[cfg(test)] +mod tests { + use super::*; + use datafusion_common::Result; + use rand::Rng; + + fn get_random_vec_i32(len: usize) -> Vec<i32> { + let mut rng = rand::thread_rng(); + let mut input = Vec::with_capacity(len); + for _i in 0..len { + input.push(rng.gen_range(0..100)); + } + input + } + + fn moving_min_i32(len: usize, n_sliding_window: usize) -> Result<()> { + let data = get_random_vec_i32(len); + let mut expected = Vec::with_capacity(len); + let mut moving_min = MovingMin::<i32>::new(); + let mut res = Vec::with_capacity(len); + for i in 0..len { + let start = i.saturating_sub(n_sliding_window); + expected.push(*data[start..i + 1].iter().min().unwrap()); + + moving_min.push(data[i]); + if i > n_sliding_window { + moving_min.pop(); + } + res.push(*moving_min.min().unwrap()); + } + assert_eq!(res, expected); + Ok(()) + } + + fn moving_max_i32(len: usize, n_sliding_window: usize) -> Result<()> { + let data = get_random_vec_i32(len); + let mut expected = Vec::with_capacity(len); + let mut moving_max = MovingMax::<i32>::new(); + let mut res = Vec::with_capacity(len); + for i in 0..len { + let start = i.saturating_sub(n_sliding_window); + expected.push(*data[start..i + 1].iter().max().unwrap()); + + moving_max.push(data[i]); + if i > n_sliding_window { + moving_max.pop(); + } + res.push(*moving_max.max().unwrap()); + } + assert_eq!(res, expected); + Ok(()) + } + + #[test] + fn moving_min_tests() -> Result<()> { Review Comment: Thank you ########## datafusion/physical-expr/src/aggregate/moving_min_max.rs: ########## @@ -0,0 +1,330 @@ +// 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. + +// The implementation is taken from https://github.com/spebern/moving_min_max/blob/master/src/lib.rs. + +//! Keep track of the minimum or maximum value in a sliding window. +//! +//! `moving min max` provides one data structure for keeping track of the +//! minimum value and one for keeping track of the maximum value in a sliding +//! window. +//! +//! Each element is stored with the current min/max. One stack to push and another one for pop. If pop stack is empty, +//! push to this stack all elements popped from first stack while updating their current min/max. Now pop from +//! the second stack (MovingMin/Max struct works as a queue). To find the minimum element of the queue, +//! look at the smallest/largest two elements of the individual stacks, then take the minimum of those two values. +//! +//! The complexity of the operations are +//! - O(1) for getting the minimum/maximum +//! - O(1) for push +//! - amortized O(1) for pop + +/// let mut moving_min = MovingMin::<i32>::new(); +/// moving_min.push(2); +/// moving_min.push(1); +/// moving_min.push(3); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(2)); +/// +/// assert_eq!(moving_min.min(), Some(&1)); +/// assert_eq!(moving_min.pop(), Some(1)); +/// +/// assert_eq!(moving_min.min(), Some(&3)); +/// assert_eq!(moving_min.pop(), Some(3)); +/// +/// assert_eq!(moving_min.min(), None); +/// assert_eq!(moving_min.pop(), None); +#[derive(Debug)] +pub struct MovingMin<T> { + push_stack: Vec<(T, T)>, + pop_stack: Vec<(T, T)>, +} + +impl<T: Clone + PartialOrd> Default for MovingMin<T> { + fn default() -> Self { + Self { + push_stack: Vec::new(), + pop_stack: Vec::new(), + } + } +} + +impl<T: Clone + PartialOrd> MovingMin<T> { + /// Creates a new `MovingMin` to keep track of the minimum in a sliding + /// window. + #[inline] + pub fn new() -> Self { + Self::default() + } + + /// Creates a new `MovingMin` to keep track of the minimum in a sliding + /// window with `capacity` allocated slots. + #[inline] + pub fn with_capacity(capacity: usize) -> Self { + Self { + push_stack: Vec::with_capacity(capacity), + pop_stack: Vec::with_capacity(capacity), + } + } + + /// Returns the minimum of the sliding window or `None` if the window is + /// empty. + #[inline] + pub fn min(&self) -> Option<&T> { + match (self.push_stack.last(), self.pop_stack.last()) { + (None, None) => None, + (Some((_, min)), None) => Some(min), + (None, Some((_, min))) => Some(min), + (Some((_, a)), Some((_, b))) => Some(if a < b { a } else { b }), + } + } + + /// Pushes a new element into the sliding window. + #[inline] + pub fn push(&mut self, val: T) { + self.push_stack.push(match self.push_stack.last() { + Some((_, min)) => { + if val > *min { + (val, min.clone()) + } else { + (val.clone(), val) + } + } + None => (val.clone(), val), + }); + } + + /// Removes and returns the last value of the sliding window. + #[inline] + pub fn pop(&mut self) -> Option<T> { + if self.pop_stack.is_empty() { + match self.push_stack.pop() { + Some((val, _)) => { + let mut last = (val.clone(), val); + self.pop_stack.push(last.clone()); + while let Some((val, _)) = self.push_stack.pop() { + let min = if last.1 < val { + last.1.clone() + } else { + val.clone() + }; + last = (val.clone(), min); + self.pop_stack.push(last.clone()); + } + } + None => return None, + } + } + self.pop_stack.pop().map(|(val, _)| val) + } + + /// Returns the number of elements stored in the sliding window. + #[inline] + pub fn len(&self) -> usize { + self.push_stack.len() + self.pop_stack.len() + } + + /// Returns `true` if the moving window contains no elements. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } +} + +/// let mut moving_max = MovingMax::<i32>::new(); +/// moving_max.push(2); +/// moving_max.push(3); +/// moving_max.push(1); +/// +/// assert_eq!(moving_max.max(), Some(&3)); +/// assert_eq!(moving_max.pop(), Some(2)); +/// +/// assert_eq!(moving_max.max(), Some(&3)); +/// assert_eq!(moving_max.pop(), Some(3)); +/// +/// assert_eq!(moving_max.max(), Some(&1)); +/// assert_eq!(moving_max.pop(), Some(1)); +/// +/// assert_eq!(moving_max.max(), None); +/// assert_eq!(moving_max.pop(), None); +#[derive(Debug)] +pub struct MovingMax<T> { + push_stack: Vec<(T, T)>, + pop_stack: Vec<(T, T)>, +} + +impl<T: Clone + PartialOrd> Default for MovingMax<T> { + fn default() -> Self { + Self { + push_stack: Vec::new(), + pop_stack: Vec::new(), + } + } +} + +impl<T: Clone + PartialOrd> MovingMax<T> { + /// Creates a new `MovingMax` to keep track of the maximum in a sliding window. + #[inline] + pub fn new() -> Self { + Self::default() + } + + /// Creates a new `MovingMax` to keep track of the maximum in a sliding window with + /// `capacity` allocated slots. + #[inline] + pub fn with_capacity(capacity: usize) -> Self { + Self { + push_stack: Vec::with_capacity(capacity), + pop_stack: Vec::with_capacity(capacity), + } + } + + /// Returns the maximum of the sliding window or `None` if the window is empty. + #[inline] + pub fn max(&self) -> Option<&T> { + match (self.push_stack.last(), self.pop_stack.last()) { + (None, None) => None, + (Some((_, max)), None) => Some(max), + (None, Some((_, max))) => Some(max), + (Some((_, a)), Some((_, b))) => Some(if a > b { a } else { b }), + } + } + + /// Pushes a new element into the sliding window. + #[inline] + pub fn push(&mut self, val: T) { + self.push_stack.push(match self.push_stack.last() { + Some((_, max)) => { + if val < *max { + (val, max.clone()) + } else { + (val.clone(), val) + } + } + None => (val.clone(), val), + }); + } + + /// Removes and returns the last value of the sliding window. + #[inline] + pub fn pop(&mut self) -> Option<T> { + if self.pop_stack.is_empty() { + match self.push_stack.pop() { + Some((val, _)) => { + let mut last = (val.clone(), val); + self.pop_stack.push(last.clone()); + while let Some((val, _)) = self.push_stack.pop() { + let max = if last.1 > val { + last.1.clone() + } else { + val.clone() + }; + last = (val.clone(), max); + self.pop_stack.push(last.clone()); + } + } + None => return None, + } + } + self.pop_stack.pop().map(|(val, _)| val) + } + + /// Returns the number of elements stored in the sliding window. + #[inline] + pub fn len(&self) -> usize { + self.push_stack.len() + self.pop_stack.len() + } + + /// Returns `true` if the moving window contains no elements. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } +} + +#[cfg(test)] +mod tests { + use super::*; + use datafusion_common::Result; + use rand::Rng; + + fn get_random_vec_i32(len: usize) -> Vec<i32> { + let mut rng = rand::thread_rng(); + let mut input = Vec::with_capacity(len); + for _i in 0..len { + input.push(rng.gen_range(0..100)); + } + input + } + + fn moving_min_i32(len: usize, n_sliding_window: usize) -> Result<()> { + let data = get_random_vec_i32(len); + let mut expected = Vec::with_capacity(len); + let mut moving_min = MovingMin::<i32>::new(); + let mut res = Vec::with_capacity(len); + for i in 0..len { + let start = i.saturating_sub(n_sliding_window); + expected.push(*data[start..i + 1].iter().min().unwrap()); + + moving_min.push(data[i]); + if i > n_sliding_window { + moving_min.pop(); + } + res.push(*moving_min.min().unwrap()); + } + assert_eq!(res, expected); + Ok(()) + } + + fn moving_max_i32(len: usize, n_sliding_window: usize) -> Result<()> { + let data = get_random_vec_i32(len); + let mut expected = Vec::with_capacity(len); + let mut moving_max = MovingMax::<i32>::new(); + let mut res = Vec::with_capacity(len); + for i in 0..len { + let start = i.saturating_sub(n_sliding_window); + expected.push(*data[start..i + 1].iter().max().unwrap()); 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