arrow/util/

bench_util.rs

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// 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,
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// "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.

//! Utils to make benchmarking easier

use crate::array::*;
use crate::datatypes::*;
use crate::util::test_util::seedable_rng;
use arrow_buffer::{Buffer, IntervalMonthDayNano};
use half::f16;
use rand::Rng;
use rand::SeedableRng;
use rand::distr::uniform::SampleUniform;
use rand::rng;
use rand::{
    distr::{Alphanumeric, Distribution, StandardUniform},
    prelude::StdRng,
};
use std::ops::Range;

/// Creates an random (but fixed-seeded) array of a given size and null density
pub fn create_primitive_array<T>(size: usize, null_density: f32) -> PrimitiveArray<T>
where
    T: ArrowPrimitiveType,
    StandardUniform: Distribution<T::Native>,
{
    let mut rng = seedable_rng();

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                Some(rng.random())
            }
        })
        .collect()
}

/// Creates an random (but fixed-seeded) array of a given size and null density,
/// all the values located in the given range
pub fn create_primitive_array_range<T>(
    size: usize,
    null_density: f32,
    value_range: Range<T::Native>,
) -> PrimitiveArray<T>
where
    T: ArrowPrimitiveType,
    StandardUniform: Distribution<T::Native>,
    T::Native: SampleUniform,
{
    let mut rng = seedable_rng();

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                Some(rng.random_range(value_range.clone()))
            }
        })
        .collect()
}

/// Creates a [`PrimitiveArray`] of a given `size` and `null_density`
/// filling it with random numbers generated using the provided `seed`.
pub fn create_primitive_array_with_seed<T>(
    size: usize,
    null_density: f32,
    seed: u64,
) -> PrimitiveArray<T>
where
    T: ArrowPrimitiveType,
    StandardUniform: Distribution<T::Native>,
{
    let mut rng = StdRng::seed_from_u64(seed);

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                Some(rng.random())
            }
        })
        .collect()
}

/// Creates a [`PrimitiveArray`] of a given `size` and `null_density`
/// filling it with random [`IntervalMonthDayNano`] generated using the provided `seed`.
pub fn create_month_day_nano_array_with_seed(
    size: usize,
    null_density: f32,
    seed: u64,
) -> IntervalMonthDayNanoArray {
    let mut rng = StdRng::seed_from_u64(seed);

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                Some(IntervalMonthDayNano::new(
                    rng.random(),
                    rng.random(),
                    rng.random(),
                ))
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) array of a given size and null density
pub fn create_boolean_array(size: usize, null_density: f32, true_density: f32) -> BooleanArray
where
    StandardUniform: Distribution<bool>,
{
    let mut rng = seedable_rng();
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value = rng.random::<f32>() < true_density;
                Some(value)
            }
        })
        .collect()
}

/// Creates a random array of a given size and null density based on the provided seed
pub fn create_boolean_array_with_seed(
    size: usize,
    null_density: f32,
    true_density: f32,
    seed: u64,
) -> BooleanArray
where
    StandardUniform: Distribution<bool>,
{
    let mut rng = StdRng::seed_from_u64(seed);
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value = rng.random::<f32>() < true_density;
                Some(value)
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) string array of a given size and null density.
///
/// Strings have a random length
/// between 0 and 400 alphanumeric characters. `0..400` is chosen to cover a wide range of common string lengths,
/// which have a dramatic impact on performance of some queries, e.g. LIKE/ILIKE/regex.
pub fn create_string_array<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
) -> GenericStringArray<Offset> {
    create_string_array_with_max_len(size, null_density, 400)
}

/// Creates longer string array with same prefix, the prefix should be larger than 4 bytes,
/// and the string length should be larger than 12 bytes
/// so that we can compare the performance with StringViewArray, because StringViewArray has 4 bytes inline for view
pub fn create_longer_string_array_with_same_prefix<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
) -> GenericStringArray<Offset> {
    create_string_array_with_len_range_and_prefix(size, null_density, 13, 100, "prefix_")
}

/// Creates longer string view array with same prefix, the prefix should be larger than 4 bytes,
/// and the string length should be larger than 12 bytes
/// so that we can compare the StringArray performance with StringViewArray, because StringViewArray has 4 bytes inline for view
pub fn create_longer_string_view_array_with_same_prefix(
    size: usize,
    null_density: f32,
) -> StringViewArray {
    create_string_view_array_with_len_range_and_prefix(size, null_density, 13, 100, "prefix_")
}

fn create_string_array_with_len_range_and_prefix<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
    min_str_len: usize,
    max_str_len: usize,
    prefix: &str,
) -> GenericStringArray<Offset> {
    create_string_array_with_len_range_and_prefix_and_seed(
        size,
        null_density,
        min_str_len,
        max_str_len,
        prefix,
        42,
    )
}

/// Creates a random [`GenericStringArray`] of a given `size` and `null_density`
/// filling it with random strings with lengths in the specified range,
/// all starting with the provided `prefix`, generated using the provided `seed`.
pub fn create_string_array_with_len_range_and_prefix_and_seed<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
    min_str_len: usize,
    max_str_len: usize,
    prefix: &str,
    seed: u64,
) -> GenericStringArray<Offset> {
    assert!(
        min_str_len <= max_str_len,
        "min_str_len must be <= max_str_len"
    );
    assert!(
        prefix.len() <= max_str_len,
        "Prefix length must be <= max_str_len"
    );

    let rng = &mut StdRng::seed_from_u64(seed);
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let remaining_len = rng.random_range(
                    min_str_len.saturating_sub(prefix.len())..=(max_str_len - prefix.len()),
                );

                let mut value = prefix.to_string();
                value.extend(
                    rng.sample_iter(&Alphanumeric)
                        .take(remaining_len)
                        .map(char::from),
                );

                Some(value)
            }
        })
        .collect()
}
/// Creates a string view array of a given range, null density and length
///
/// Arguments:
/// - `size`: number of  string view array
/// - `null_density`: density of nulls in the string view array
/// - `range`: range size of each string in the string view array
/// - `seed`: seed for the random number generator
pub fn create_string_view_array_with_len_range_and_seed(
    size: usize,
    null_density: f32,
    range: Range<usize>,
    seed: u64,
) -> StringViewArray {
    let rng = &mut StdRng::seed_from_u64(seed);
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let str_len = rng.random_range(range.clone());
                let value = rng.sample_iter(&Alphanumeric).take(str_len).collect();
                let value = String::from_utf8(value).unwrap();
                Some(value)
            }
        })
        .collect()
}

fn create_string_view_array_with_len_range_and_prefix(
    size: usize,
    null_density: f32,
    min_str_len: usize,
    max_str_len: usize,
    prefix: &str,
) -> StringViewArray {
    assert!(
        min_str_len <= max_str_len,
        "min_str_len must be <= max_str_len"
    );
    assert!(
        prefix.len() <= max_str_len,
        "Prefix length must be <= max_str_len"
    );

    let rng = &mut seedable_rng();
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let remaining_len = rng.random_range(
                    min_str_len.saturating_sub(prefix.len())..=(max_str_len - prefix.len()),
                );

                let mut value = prefix.to_string();
                value.extend(
                    rng.sample_iter(&Alphanumeric)
                        .take(remaining_len)
                        .map(char::from),
                );

                Some(value)
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) array of rand size with a given max size, null density and length
pub fn create_string_array_with_max_len<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
    max_str_len: usize,
) -> GenericStringArray<Offset> {
    let rng = &mut seedable_rng();
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let str_len = rng.random_range(0..max_str_len);
                let value = rng.sample_iter(&Alphanumeric).take(str_len).collect();
                let value = String::from_utf8(value).unwrap();
                Some(value)
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) array of a given size, null density and length
pub fn create_string_array_with_len<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
    str_len: usize,
) -> GenericStringArray<Offset> {
    let rng = &mut seedable_rng();

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value = rng.sample_iter(&Alphanumeric).take(str_len).collect();
                let value = String::from_utf8(value).unwrap();
                Some(value)
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) string view array of a given size and null density.
///
/// See `create_string_array` above for more details.
pub fn create_string_view_array(size: usize, null_density: f32) -> StringViewArray {
    create_string_view_array_with_max_len(size, null_density, 400)
}

/// Creates a random (but fixed-seeded) array of rand size with a given max size, null density and length
pub fn create_string_view_array_with_max_len(
    size: usize,
    null_density: f32,
    max_str_len: usize,
) -> StringViewArray {
    let rng = &mut seedable_rng();
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let str_len = rng.random_range(0..max_str_len);
                let value = rng.sample_iter(&Alphanumeric).take(str_len).collect();
                let value = String::from_utf8(value).unwrap();
                Some(value)
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) array of a given size, null density and length
pub fn create_string_view_array_with_fixed_len(
    size: usize,
    null_density: f32,
    str_len: usize,
) -> StringViewArray {
    let rng = &mut seedable_rng();
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value = rng.sample_iter(&Alphanumeric).take(str_len).collect();
                let value = String::from_utf8(value).unwrap();
                Some(value)
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) array of a given size, null density and length
pub fn create_string_view_array_with_len(
    size: usize,
    null_density: f32,
    str_len: usize,
    mixed: bool,
) -> StringViewArray {
    let rng = &mut seedable_rng();

    let mut lengths = Vec::with_capacity(size);

    // if mixed, we creates first half that string length small than 12 bytes and second half large than 12 bytes
    if mixed {
        for _ in 0..size / 2 {
            lengths.push(rng.random_range(1..12));
        }
        for _ in size / 2..size {
            lengths.push(rng.random_range(12..=std::cmp::max(30, str_len)));
        }
    } else {
        lengths.resize(size, str_len);
    }

    lengths
        .into_iter()
        .map(|len| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value: Vec<u8> = rng.sample_iter(&Alphanumeric).take(len).collect();
                Some(String::from_utf8(value).unwrap())
            }
        })
        .collect()
}

/// Creates an random (but fixed-seeded) array of a given size and null density
/// consisting of random 4 character alphanumeric strings
pub fn create_string_dict_array<K: ArrowDictionaryKeyType>(
    size: usize,
    null_density: f32,
    str_len: usize,
) -> DictionaryArray<K> {
    let rng = &mut seedable_rng();

    let data: Vec<_> = (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value = rng.sample_iter(&Alphanumeric).take(str_len).collect();
                let value = String::from_utf8(value).unwrap();
                Some(value)
            }
        })
        .collect();

    data.iter().map(|x| x.as_deref()).collect()
}

/// Create a List/LargeList Array  of primitive values
///
/// Arguments:
/// - `size`: number of lists in the array
/// - `null_density`: density of nulls in the list array
/// - `list_null_density`: density of nulls in the primitive arrays inside the lists
/// - `max_list_size`: maximum size of each list (actual size is random between 0 and max_list_size)
/// - `seed`: seed for the random number generator
pub fn create_primitive_list_array_with_seed<O, T>(
    size: usize,
    null_density: f32,
    list_null_density: f32,
    max_list_size: usize,
    seed: u64,
) -> GenericListArray<O>
where
    O: OffsetSizeTrait,
    T: ArrowPrimitiveType,
    StandardUniform: Distribution<T::Native>,
{
    let mut rng = StdRng::seed_from_u64(seed);

    let values = (0..size).map(|_| {
        if rng.random::<f32>() < null_density {
            None
        } else {
            let list_size = rng.random_range(0..=max_list_size);
            let list_values: Vec<Option<T::Native>> = (0..list_size)
                .map(|_| {
                    if rng.random::<f32>() < list_null_density {
                        None
                    } else {
                        Some(rng.random())
                    }
                })
                .collect();
            Some(list_values)
        }
    });

    GenericListArray::<O>::from_iter_primitive::<T, _, _>(values)
}

/// Create a List/LargeList Array of primitive values using a fixed seed
///
/// See [`create_primitive_list_array_with_seed`] for details on arguments.
pub fn create_primitive_list_array<O, T>(
    size: usize,
    null_density: f32,
    list_null_density: f32,
    max_list_size: usize,
) -> GenericListArray<O>
where
    O: OffsetSizeTrait,
    T: ArrowPrimitiveType,
    StandardUniform: Distribution<T::Native>,
{
    let mut rng = seedable_rng();

    let values = (0..size).map(|_| {
        if rng.random::<f32>() < null_density {
            None
        } else {
            let list_size = rng.random_range(0..=max_list_size);
            let list_values: Vec<Option<T::Native>> = (0..list_size)
                .map(|_| {
                    if rng.random::<f32>() < list_null_density {
                        None
                    } else {
                        Some(rng.random())
                    }
                })
                .collect();
            Some(list_values)
        }
    });

    GenericListArray::<O>::from_iter_primitive::<T, _, _>(values)
}

/// Create a ListViewArray of primitive values using a fixed seed
///
/// See [`create_primitive_list_array_with_seed`] for details on arguments.
pub fn create_primitive_list_view_array<O, T>(
    size: usize,
    null_density: f32,
    list_null_density: f32,
    max_list_size: usize,
) -> GenericListViewArray<O>
where
    T: ArrowPrimitiveType,
    StandardUniform: Distribution<T::Native>,
    O: OffsetSizeTrait,
{
    let mut rng = seedable_rng();

    let values = (0..size).map(|_| {
        if rng.random::<f32>() < null_density {
            None
        } else {
            let list_size = rng.random_range(0..=max_list_size);
            let list_values: Vec<Option<T::Native>> = (0..list_size)
                .map(|_| {
                    if rng.random::<f32>() < list_null_density {
                        None
                    } else {
                        Some(rng.random())
                    }
                })
                .collect();
            Some(list_values)
        }
    });

    GenericListViewArray::<O>::from_iter_primitive::<T, _, _>(values)
}

/// Create primitive run array for given logical and physical array lengths
pub fn create_primitive_run_array<R: RunEndIndexType, V: ArrowPrimitiveType>(
    logical_array_len: usize,
    physical_array_len: usize,
) -> RunArray<R> {
    assert!(logical_array_len >= physical_array_len);
    // typical length of each run
    let run_len = logical_array_len / physical_array_len;

    // Some runs should have extra length
    let mut run_len_extra = logical_array_len % physical_array_len;

    let mut values: Vec<V::Native> = (0..physical_array_len)
        .flat_map(|s| {
            let mut take_len = run_len;
            if run_len_extra > 0 {
                take_len += 1;
                run_len_extra -= 1;
            }
            std::iter::repeat_n(V::Native::from_usize(s).unwrap(), take_len)
        })
        .collect();
    while values.len() < logical_array_len {
        let last_val = values[values.len() - 1];
        values.push(last_val);
    }
    let mut builder = PrimitiveRunBuilder::<R, V>::with_capacity(physical_array_len);
    builder.extend(values.into_iter().map(Some));

    builder.finish()
}

/// Create string array to be used by run array builder. The string array
/// will result in run array with physical length of `physical_array_len`
/// and logical length of `logical_array_len`
pub fn create_string_array_for_runs(
    physical_array_len: usize,
    logical_array_len: usize,
    string_len: usize,
) -> Vec<String> {
    assert!(logical_array_len >= physical_array_len);
    let mut rng = rng();

    // typical length of each run
    let run_len = logical_array_len / physical_array_len;

    // Some runs should have extra length
    let mut run_len_extra = logical_array_len % physical_array_len;

    let mut values: Vec<String> = (0..physical_array_len)
        .map(|_| (0..string_len).map(|_| rng.random::<char>()).collect())
        .flat_map(|s| {
            let mut take_len = run_len;
            if run_len_extra > 0 {
                take_len += 1;
                run_len_extra -= 1;
            }
            std::iter::repeat_n(s, take_len)
        })
        .collect();
    while values.len() < logical_array_len {
        let last_val = values[values.len() - 1].clone();
        values.push(last_val);
    }
    values
}

/// Creates an random (but fixed-seeded) binary array of a given size and null density
pub fn create_binary_array<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
) -> GenericBinaryArray<Offset> {
    create_binary_array_with_seed(
        size,
        null_density,
        42, // bytes_seed
        42, // bytes_length_seed
    )
}

/// Creates a random [`GenericBinaryArray`] of a given `size` and `null_density`
/// filling it with random bytes, generated using the provided `seed`s.
///
/// the `bytes_seed` is used to seed the RNG for generating the byte values,
/// while the `bytes_length_seed` is used to seed the RNG for generating the length of an array item
///
/// These values can be the same as they are used to seed different RNGs internally.
pub fn create_binary_array_with_seed<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
    bytes_seed: u64,
    bytes_length_seed: u64,
) -> GenericBinaryArray<Offset> {
    let rng = &mut StdRng::seed_from_u64(bytes_seed);
    let range_rng = &mut StdRng::seed_from_u64(bytes_length_seed);

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value = rng
                    .sample_iter::<u8, _>(StandardUniform)
                    .take(range_rng.random_range(0..8))
                    .collect::<Vec<u8>>();
                Some(value)
            }
        })
        .collect()
}

/// Creates a random [`GenericBinaryArray`] of a given `size` and `null_density`
/// filling it with random bytes with lengths in the specified range,
/// all starting with the provided `prefix`, generated using the provided `seed`.
///
pub fn create_binary_array_with_len_range_and_prefix_and_seed<Offset: OffsetSizeTrait>(
    size: usize,
    null_density: f32,
    min_len: usize,
    max_len: usize,
    prefix: &[u8],
    seed: u64,
) -> GenericBinaryArray<Offset> {
    assert!(min_len <= max_len, "min_len must be <= max_len");
    assert!(prefix.len() <= max_len, "Prefix length must be <= max_len");

    let rng = &mut StdRng::seed_from_u64(seed);
    (0..size)
        .map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let remaining_len = rng
                    .random_range(min_len.saturating_sub(prefix.len())..=(max_len - prefix.len()));

                let remaining = rng
                    .sample_iter::<u8, _>(StandardUniform)
                    .take(remaining_len);

                let value = prefix.iter().copied().chain(remaining).collect::<Vec<u8>>();
                Some(value)
            }
        })
        .collect()
}

/// Creates an random (but fixed-seeded) array of a given size and null density
pub fn create_fsb_array(size: usize, null_density: f32, value_len: usize) -> FixedSizeBinaryArray {
    let rng = &mut seedable_rng();

    FixedSizeBinaryArray::try_from_sparse_iter_with_size(
        (0..size).map(|_| {
            if rng.random::<f32>() < null_density {
                None
            } else {
                let value = rng
                    .sample_iter::<u8, _>(StandardUniform)
                    .take(value_len)
                    .collect::<Vec<u8>>();
                Some(value)
            }
        }),
        value_len as i32,
    )
    .unwrap()
}

/// Creates a random (but fixed-seeded) dictionary array of a given size and null density
/// with the provided values array
pub fn create_dict_from_values<K>(
    size: usize,
    null_density: f32,
    values: &dyn Array,
) -> DictionaryArray<K>
where
    K: ArrowDictionaryKeyType,
    StandardUniform: Distribution<K::Native>,
    K::Native: SampleUniform,
{
    let min_key = K::Native::from_usize(0).unwrap();
    let max_key = K::Native::from_usize(values.len()).unwrap();
    create_sparse_dict_from_values(size, null_density, values, min_key..max_key)
}

/// Creates a random (but fixed-seeded) dictionary array of a given size and null density
/// with the provided values array and key range
pub fn create_sparse_dict_from_values<K>(
    size: usize,
    null_density: f32,
    values: &dyn Array,
    key_range: Range<K::Native>,
) -> DictionaryArray<K>
where
    K: ArrowDictionaryKeyType,
    StandardUniform: Distribution<K::Native>,
    K::Native: SampleUniform,
{
    let mut rng = seedable_rng();
    let data_type =
        DataType::Dictionary(Box::new(K::DATA_TYPE), Box::new(values.data_type().clone()));

    let keys: Buffer = (0..size)
        .map(|_| rng.random_range(key_range.clone()))
        .collect();

    let nulls: Option<Buffer> = (null_density != 0.).then(|| {
        (0..size)
            .map(|_| rng.random_bool(null_density as _))
            .collect()
    });

    let data = ArrayDataBuilder::new(data_type)
        .len(size)
        .null_bit_buffer(nulls)
        .add_buffer(keys)
        .add_child_data(values.to_data())
        .build()
        .unwrap();

    DictionaryArray::from(data)
}

/// Creates a random (but fixed-seeded) f16 array of a given size and nan-value density
pub fn create_f16_array(size: usize, nan_density: f32) -> Float16Array {
    let mut rng = seedable_rng();

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < nan_density {
                Some(f16::NAN)
            } else {
                Some(rng.random())
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) f32 array of a given size and nan-value density
pub fn create_f32_array(size: usize, nan_density: f32) -> Float32Array {
    let mut rng = seedable_rng();

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < nan_density {
                Some(f32::NAN)
            } else {
                Some(rng.random())
            }
        })
        .collect()
}

/// Creates a random (but fixed-seeded) f64 array of a given size and nan-value density
pub fn create_f64_array(size: usize, nan_density: f32) -> Float64Array {
    let mut rng = seedable_rng();

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < nan_density {
                Some(f64::NAN)
            } else {
                Some(rng.random())
            }
        })
        .collect()
}

/// Creates a random f64 array of a given size and nan-value density based on a given seed
pub fn create_f64_array_with_seed(size: usize, nan_density: f32, seed: u64) -> Float64Array {
    let mut rng = StdRng::seed_from_u64(seed);

    (0..size)
        .map(|_| {
            if rng.random::<f32>() < nan_density {
                Some(f64::NAN)
            } else {
                Some(rng.random())
            }
        })
        .collect()
}