concat_elements.rs

// 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 crate::array::*;
use crate::compute::util::combine_option_bitmap;
use crate::error::{ArrowError, Result};

/// Returns the elementwise concatenation of a [`StringArray`].
///
/// An index of the resulting [`StringArray`] is null if any of
/// `StringArray` are null at that location.
///
/// ```text
/// e.g:
///
///   ["Hello"] + ["World"] = ["HelloWorld"]
///
///   ["a", "b"] + [None, "c"] + [None, "d"] = [None, "bcd"]
/// ```
///
/// An error will be returned if the [`StringArray`] are of different lengths.
pub fn concat_elements_utf8<Offset: OffsetSizeTrait>(
    arrays: &[&GenericStringArray<Offset>],
) -> Result<GenericStringArray<Offset>> {
    if arrays.len() < 2 {
        return Err(ArrowError::ComputeError(format!(
            "Arrays must have at least two elements length: {}",
            arrays.len(),
        )));
    }

    let size = arrays[0].len();
    if !arrays.iter().all(|array| array.len() == size) {
        return Err(ArrowError::ComputeError(format!(
            "Arrays must have the same length of {}",
            size,
        )));
    }

    let output_bitmap = combine_option_bitmap(
        arrays
            .iter()
            .map(|a| a.data())
            .collect::<Vec<_>>()
            .as_slice(),
        size,
    )?;

    let data_buffers = arrays
        .iter()
        .map(|array| array.value_data())
        .collect::<Vec<_>>();

    let data_values = data_buffers
        .iter()
        .map(|buffer| buffer.as_slice())
        .collect::<Vec<_>>();

    let mut offsets = arrays
        .iter()
        .map(|a| a.value_offsets().iter().peekable())
        .collect::<Vec<_>>();

    let mut output_values = BufferBuilder::<u8>::new(
        data_values
            .iter()
            .zip(offsets.iter_mut())
            .map(|(data, offset)| data.len() - offset.peek().unwrap().to_usize().unwrap())
            .sum(),
    );

    let mut output_offsets = BufferBuilder::<Offset>::new(size + 1);
    output_offsets.append(Offset::zero());
    for _ in 0..size {
        data_values
            .iter()
            .zip(offsets.iter_mut())
            .for_each(|(values, offset)| {
                let index_start = offset.next().unwrap().to_usize().unwrap();
                let index_end = offset.peek().unwrap().to_usize().unwrap();
                output_values.append_slice(&values[index_start..index_end]);
            });
        output_offsets.append(Offset::from_usize(output_values.len()).unwrap());
    }

    let builder = ArrayDataBuilder::new(GenericStringArray::<Offset>::get_data_type())
        .len(size)
        .add_buffer(output_offsets.finish())
        .add_buffer(output_values.finish())
        .null_bit_buffer(output_bitmap);

    // SAFETY - offsets valid by construction
    Ok(unsafe { builder.build_unchecked() }.into())
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_string_concat() {
        let left = [Some("foo"), Some("bar"), None]
            .into_iter()
            .collect::<StringArray>();
        let right = [None, Some("yyy"), Some("zzz")]
            .into_iter()
            .collect::<StringArray>();

        let output = concat_elements_utf8(&[&left, &right]).unwrap();

        let expected = [None, Some("baryyy"), None]
            .into_iter()
            .collect::<StringArray>();

        assert_eq!(output, expected);
    }

    #[test]
    fn test_string_concat_empty_string() {
        let left = [Some("foo"), Some(""), Some("bar")]
            .into_iter()
            .collect::<StringArray>();
        let right = [Some("baz"), Some(""), Some("")]
            .into_iter()
            .collect::<StringArray>();

        let output = concat_elements_utf8(&[&left, &right]).unwrap();

        let expected = [Some("foobaz"), Some(""), Some("bar")]
            .into_iter()
            .collect::<StringArray>();

        assert_eq!(output, expected);
    }

    #[test]
    fn test_string_concat_no_null() {
        let left = StringArray::from(vec!["foo", "bar"]);
        let right = StringArray::from(vec!["bar", "baz"]);

        let output = concat_elements_utf8(&[&left, &right]).unwrap();

        let expected = StringArray::from(vec!["foobar", "barbaz"]);

        assert_eq!(output, expected);
    }

    #[test]
    fn test_string_concat_error_array_length() {
        let left = StringArray::from(vec!["foo", "bar"]);
        let right = StringArray::from(vec!["baz"]);

        let output = concat_elements_utf8(&[&left, &right]);

        assert_eq!(
            output.unwrap_err().to_string(),
            "Compute error: Arrays must have the same length of 2".to_string()
        );
    }

    #[test]
    fn test_string_concat_error_slice_length() {
        let left = [Some("foo"), Some("bar"), None]
            .into_iter()
            .collect::<StringArray>();
        assert_eq!(
            concat_elements_utf8(&[&left]).unwrap_err().to_string(),
            "Compute error: Arrays must have at least two elements length: 1".to_string()
        );
    }

    #[test]
    fn test_string_concat_multiple() {
        let foo = StringArray::from(vec![Some("f"), Some("o"), Some("o"), None]);
        let bar = StringArray::from(vec![None, Some("b"), Some("a"), Some("r")]);
        let baz = StringArray::from(vec![Some("b"), None, Some("a"), Some("z")]);

        let output = concat_elements_utf8(&[&foo, &bar, &baz]).unwrap();

        let expected = [None, None, Some("oaa"), None]
            .into_iter()
            .collect::<StringArray>();

        assert_eq!(output, expected);
    }

    #[test]
    fn test_string_concat_slice() {
        let left = &StringArray::from(vec![None, Some("foo"), Some("bar"), Some("baz")]);
        let right = &StringArray::from(vec![Some("boo"), None, Some("far"), Some("faz")]);

        let left_slice = left.slice(0, 3);
        let right_slice = right.slice(1, 3);
        let output = concat_elements_utf8(&[
            left_slice
                .as_any()
                .downcast_ref::<GenericStringArray<i32>>()
                .unwrap(),
            right_slice
                .as_any()
                .downcast_ref::<GenericStringArray<i32>>()
                .unwrap(),
        ])
        .unwrap();

        let expected = [None, Some("foofar"), Some("barfaz")]
            .into_iter()
            .collect::<StringArray>();

        assert_eq!(output, expected);

        let left_slice = left.slice(2, 2);
        let right_slice = right.slice(1, 2);

        let output = concat_elements_utf8(&[
            left_slice
                .as_any()
                .downcast_ref::<GenericStringArray<i32>>()
                .unwrap(),
            right_slice
                .as_any()
                .downcast_ref::<GenericStringArray<i32>>()
                .unwrap(),
        ])
        .unwrap();

        let expected = [None, Some("bazfar")].into_iter().collect::<StringArray>();

        assert_eq!(output, expected);
    }
}