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top_k.rs
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top_k.rs
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use std::cmp::Ordering;
use arrow::array::{BooleanArray, MutableBooleanArray};
use arrow::bitmap::MutableBitmap;
use either::Either;
use polars_core::downcast_as_macro_arg_physical;
use polars_core::prelude::*;
use polars_utils::total_ord::TotalOrd;
fn arg_partition<T, C: Fn(&T, &T) -> Ordering>(
v: &mut [T],
k: usize,
descending: bool,
cmp: C,
) -> &[T] {
let (lower, _el, upper) = v.select_nth_unstable_by(k, &cmp);
if descending {
lower.sort_unstable_by(cmp);
lower
} else {
upper.sort_unstable_by(|a, b| cmp(b, a));
upper
}
}
fn top_k_num_impl<T>(ca: &ChunkedArray<T>, k: usize, descending: bool) -> ChunkedArray<T>
where
T: PolarsNumericType,
ChunkedArray<T>: ChunkSort<T>,
{
if k >= ca.len() {
return ca.sort(!descending);
}
// descending is opposite from sort as top-k returns largest
let k = if descending {
std::cmp::min(k, ca.len())
} else {
ca.len().saturating_sub(k + 1)
};
match ca.to_vec_null_aware() {
Either::Left(mut v) => {
let values = arg_partition(&mut v, k, descending, TotalOrd::tot_cmp);
ChunkedArray::from_slice(ca.name(), values)
},
Either::Right(mut v) => {
let values = arg_partition(&mut v, k, descending, TotalOrd::tot_cmp);
let mut out = ChunkedArray::from_iter(values.iter().copied());
out.rename(ca.name());
out
},
}
}
fn top_k_bool_impl(
ca: &ChunkedArray<BooleanType>,
k: usize,
descending: bool,
) -> ChunkedArray<BooleanType> {
if ca.null_count() == 0 {
let true_count = ca.sum().unwrap() as usize;
let mut bitmap = MutableBitmap::with_capacity(k);
if !descending {
// true first
bitmap.extend_constant(std::cmp::min(k, true_count), true);
bitmap.extend_constant(k.saturating_sub(true_count), false);
} else {
let false_count = ca.len().saturating_sub(true_count);
bitmap.extend_constant(std::cmp::min(k, false_count), false);
bitmap.extend_constant(k.saturating_sub(false_count), true);
}
let arr = BooleanArray::from_data_default(bitmap.into(), None);
unsafe {
ChunkedArray::from_chunks_and_dtype(ca.name(), vec![Box::new(arr)], DataType::Boolean)
}
} else {
let null_count = ca.null_count();
let true_count = ca.sum().unwrap() as usize;
let false_count = ca.len() - true_count - null_count;
let mut remaining = k;
fn extend_constant_check_remaining(
array: &mut MutableBooleanArray,
remaining: &mut usize,
additional: usize,
value: Option<bool>,
) {
array.extend_constant(std::cmp::min(additional, *remaining), value);
*remaining = remaining.saturating_sub(additional);
}
let mut array = MutableBooleanArray::with_capacity(k);
if !descending {
// Null -> True -> False
extend_constant_check_remaining(&mut array, &mut remaining, null_count, None);
extend_constant_check_remaining(&mut array, &mut remaining, true_count, Some(true));
extend_constant_check_remaining(&mut array, &mut remaining, false_count, Some(false));
} else {
// False -> True -> Null
extend_constant_check_remaining(&mut array, &mut remaining, false_count, Some(false));
extend_constant_check_remaining(&mut array, &mut remaining, true_count, Some(true));
extend_constant_check_remaining(&mut array, &mut remaining, null_count, None);
}
let mut new_ca: ChunkedArray<BooleanType> = BooleanArray::from(array).into();
new_ca.rename(ca.name());
new_ca
}
}
fn top_k_binary_impl(
ca: &ChunkedArray<BinaryType>,
k: usize,
descending: bool,
) -> ChunkedArray<BinaryType> {
if k >= ca.len() {
return ca.sort(!descending);
}
// descending is opposite from sort as top-k returns largest
let k = if descending {
std::cmp::min(k, ca.len())
} else {
ca.len().saturating_sub(k + 1)
};
if ca.null_count() == 0 {
let mut v: Vec<&[u8]> = Vec::with_capacity(ca.len());
for arr in ca.downcast_iter() {
v.extend(arr.non_null_values_iter());
}
let values = arg_partition(&mut v, k, descending, TotalOrd::tot_cmp);
ChunkedArray::from_slice(ca.name(), values)
} else {
let mut v = Vec::with_capacity(ca.len());
for arr in ca.downcast_iter() {
v.extend(arr.iter());
}
let values = arg_partition(&mut v, k, descending, TotalOrd::tot_cmp);
let mut out = ChunkedArray::from_iter(values.iter().copied());
out.rename(ca.name());
out
}
}
pub fn top_k(s: &[Series], descending: bool) -> PolarsResult<Series> {
let k_s = &s[1];
polars_ensure!(
k_s.len() == 1,
ComputeError: "`k` must be a single value for `top_k`."
);
let Some(k) = k_s.cast(&IDX_DTYPE)?.idx()?.get(0) else {
polars_bail!(ComputeError: "`k` must be set for `top_k`")
};
let src = &s[0];
if src.is_empty() {
return Ok(src.clone());
}
match src.is_sorted_flag() {
polars_core::series::IsSorted::Ascending => {
// TopK is the k element in the bottom of ascending sorted array
return Ok(src
.slice((src.len() - k as usize) as i64, k as usize)
.reverse());
},
polars_core::series::IsSorted::Descending => {
return Ok(src.slice(0, k as usize));
},
_ => {},
}
let origin_dtype = src.dtype();
let s = src.to_physical_repr();
match s.dtype() {
DataType::Boolean => {
Ok(top_k_bool_impl(s.bool().unwrap(), k as usize, descending).into_series())
},
DataType::String => {
let ca = top_k_binary_impl(&s.str().unwrap().as_binary(), k as usize, descending);
let ca = unsafe { ca.to_string() };
Ok(ca.into_series())
},
DataType::Binary => {
Ok(top_k_binary_impl(s.binary().unwrap(), k as usize, descending).into_series())
},
_dt => {
macro_rules! dispatch {
($ca:expr) => {{
top_k_num_impl($ca, k as usize, descending).into_series()
}};
}
unsafe { downcast_as_macro_arg_physical!(&s, dispatch).cast_unchecked(origin_dtype) }
},
}
}