jorgecarleitao commented on a change in pull request #9381: URL: https://github.com/apache/arrow/pull/9381#discussion_r571416880
########## File path: rust/arrow/src/compute/kernels/window.rs ########## @@ -0,0 +1,110 @@ +// 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. + +//! Defines windowing functions, like `shift`ing + +use crate::compute::concat; +use num::{abs, clamp}; +use std::sync::Arc; + +use crate::{ + array::{make_array, ArrayData, PrimitiveArray}, + datatypes::ArrowPrimitiveType, + error::Result, +}; +use crate::{ + array::{Array, ArrayRef}, + buffer::MutableBuffer, +}; + +/// Shifts array by defined number of items (to left or right) +/// A positive value for `offset` shifts the array to the right +/// a negative value shifts the array to the left. +/// # Examples +/// ``` +/// use arrow::array::Int32Array; +/// use arrow::error::Result; +/// use arrow::compute::shift; +/// +/// let a: Int32Array = vec![Some(1), None, Some(4)].into(); +/// // shift array 1 element to the right +/// let res = shift(&a, 1).unwrap(); +/// let expected: Int32Array = vec![None, Some(1), None].into(); +/// assert_eq!(res.as_ref(), &expected) +/// ``` +pub fn shift<T>(values: &PrimitiveArray<T>, offset: i64) -> Result<ArrayRef> +where + T: ArrowPrimitiveType, +{ + // Compute slice + let slice_offset = clamp(-offset, 0, values.len() as i64) as usize; + let length = values.len() - abs(offset) as usize; + let slice = values.slice(slice_offset, length); + + // Generate array with remaining `null` items + let nulls = abs(offset as i64) as usize; + + let mut null_array = MutableBuffer::new(nulls); + let mut null_data = MutableBuffer::new(nulls * T::get_byte_width()); + null_array.extend_zeros(nulls); + null_data.extend_zeros(nulls * T::get_byte_width()); + + let null_data = ArrayData::new( + T::DATA_TYPE, + nulls as usize, + Some(nulls), + Some(null_array.into()), Review comment: I did not have time to go through this, but I get the feeling that this buffer may be too large: imo it should be `ceil(nulls, 8)`, since there are 8 slots per byte for bitmaps, no? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
