Windowed std does not work correctly (non-deterministic, incorrect values)

[erinov1]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

import polars as pl

c1 = pl.DataFrame({"A": [1, 1], "B": [1.0, 2.0]})
c2 = pl.DataFrame({"A": [2, 2], "B": [1.0, 2.0]})

df = pl.concat([c1, c2], rechunk=False)

df.select(pl.col("B").std().over("A").alias("std"))

Log output

No response

Issue description

The query df.select(pl.col("B").std().over("A").alias("std")) above returns a variety of incorrect, non-deterministic values, for example

shape: (4, 1)
┌────────────┐
│ std        │
│ ---        │
│ f64        │
╞════════════╡
│ 0.707107   │
│ 0.707107   │
│ 3.6788e-90 │
│ 3.6788e-90 │
└────────────┘

shape: (4, 1)
┌─────────────┐
│ std         │
│ ---         │
│ f64         │
╞═════════════╡
│ 0.707107    │
│ 0.707107    │
│ 4.2522e-154 │
│ 4.2522e-154 │
└─────────────┘

This is only an issue when multiple chunks are present. Rechunking fixes the issue. The query also works correctly if std() is replaced with var().pow(1/2), even for multiple chunks.

Expected behavior

The query should return the correct answer

shape: (4, 1)
┌──────────┐
│ std      │
│ ---      │
│ f64      │
╞══════════╡
│ 0.707107 │
│ 0.707107 │
│ 0.707107 │
│ 0.707107 │
└──────────┘

Installed versions

--------Version info---------
Polars:               0.20.31
Index type:           UInt32
Platform:             macOS-14.4.1-arm64-arm-64bit
Python:               3.11.1 (main, Feb  8 2023, 16:32:14) [Clang 14.0.0 (clang-1400.0.29.202)]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          <not installed>
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            <not installed>
fsspec:               2023.12.2
gevent:               <not installed>
hvplot:               <not installed>
matplotlib:           3.7.4
nest_asyncio:         1.6.0
numpy:                1.24.4
openpyxl:             <not installed>
pandas:               1.5.3
pyarrow:              12.0.1
pydantic:             1.10.14
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           2.0.25
torch:                <not installed>
xlsx2csv:             <not installed>
xlsxwriter:           <not installed>

[nameexhaustion]

This panics on a debug build for OOB slice access:

   7: polars_arrow::legacy::kernels::take_agg::var::take_var_no_null_primitive_iter_unchecked::{{closure}}
             at ./crates/polars-arrow/src/legacy/kernels/take_agg/var.rs:58:26

Full backtrace

thread 'polars-0' panicked at library/core/src/panicking.rs:219:5:
unsafe precondition(s) violated: slice::get_unchecked requires that the index is within the slice
stack backtrace:
   0: rust_begin_unwind
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/std/src/panicking.rs:652:5
   1: core::panicking::panic_nounwind_fmt::runtime
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/panicking.rs:110:18
   2: core::panicking::panic_nounwind_fmt
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/panicking.rs:120:5
   3: core::panicking::panic_nounwind
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/panicking.rs:219:5
   4: <usize as core::slice::index::SliceIndex<[T]>>::get_unchecked::precondition_check
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/ub_checks.rs:68:21
   5: <usize as core::slice::index::SliceIndex<[T]>>::get_unchecked
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/ub_checks.rs:75:17
   6: core::slice::<impl [T]>::get_unchecked
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/slice/mod.rs:686:20
   7: polars_arrow::legacy::kernels::take_agg::var::take_var_no_null_primitive_iter_unchecked::{{closure}}
             at ./crates/polars-arrow/src/legacy/kernels/take_agg/var.rs:58:26
   8: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/ops/function.rs:305:13
   9: core::option::Option<T>::map
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/option.rs:1075:29
  10: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::next
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/iter/adapters/map.rs:108:26
  11: polars_arrow::legacy::kernels::take_agg::var::online_variance
             at ./crates/polars-arrow/src/legacy/kernels/take_agg/var.rs:23:18
  12: polars_arrow::legacy::kernels::take_agg::var::take_var_no_null_primitive_iter_unchecked
             at ./crates/polars-arrow/src/legacy/kernels/take_agg/var.rs:62:5
  13: polars_core::frame::group_by::aggregations::<impl polars_core::series::implementations::SeriesWrap<polars_core::chunked_array::ChunkedArray<T>>>::agg_std::{{closure}}
             at ./crates/polars-core/src/frame/group_by/aggregations/mod.rs:849:25
  14: core::ops::function::impls::<impl core::ops::function::FnMut<A> for &F>::call_mut
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/ops/function.rs:272:13
  15: core::iter::adapters::map::map_try_fold::{{closure}}
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/iter/adapters/map.rs:96:28
  16: core::iter::traits::iterator::Iterator::try_fold
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/iter/traits/iterator.rs:2411:21
  17: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/iter/adapters/map.rs:122:9
  18: <core::iter::adapters::take_while::TakeWhile<I,P> as core::iter::traits::iterator::Iterator>::try_fold
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/iter/adapters/take_while.rs:94:13
  19: <core::iter::adapters::take_while::TakeWhile<I,P> as core::iter::traits::iterator::Iterator>::fold
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/iter/mod.rs:378:13
  20: <rayon::iter::fold::FoldFolder<C,ID,F> as rayon::iter::plumbing::Folder<T>>::consume_iter
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-1.10.0/src/iter/fold.rs:158:20
  21: <rayon::iter::map::MapFolder<C,F> as rayon::iter::plumbing::Folder<T>>::consume_iter
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-1.10.0/src/iter/map.rs:248:21
  22: rayon::iter::plumbing::Producer::fold_with
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-1.10.0/src/iter/plumbing/mod.rs:109:9
  23: rayon::iter::plumbing::bridge_producer_consumer::helper
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-1.10.0/src/iter/plumbing/mod.rs:437:13
  24: rayon::iter::plumbing::bridge_producer_consumer::helper::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-1.10.0/src/iter/plumbing/mod.rs:426:21
  25: rayon_core::join::join_context::call_b::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/join/mod.rs:129:25
  26: rayon_core::job::JobResult<T>::call::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:218:41
  27: <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/panic/unwind_safe.rs:272:9
  28: std::panicking::try::do_call
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/std/src/panicking.rs:559:40
  29: ___rust_try
  30: std::panicking::try
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/std/src/panicking.rs:523:19
  31: std::panic::catch_unwind
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/std/src/panic.rs:149:14
  32: rayon_core::unwind::halt_unwinding
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/unwind.rs:17:5
  33: rayon_core::job::JobResult<T>::call
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:218:15
  34: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:120:32
  35: rayon_core::job::JobRef::execute
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:64:9
  36: rayon_core::registry::WorkerThread::execute
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:860:9
  37: rayon_core::registry::WorkerThread::wait_until_cold
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:794:21
  38: rayon_core::registry::WorkerThread::wait_until
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:769:13
  39: rayon_core::join::join_context::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/join/mod.rs:167:17
  40: rayon_core::registry::in_worker
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:951:13
  41: rayon_core::join::join_context
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/join/mod.rs:132:5
  42: rayon_core::join::join
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/join/mod.rs:105:5
  43: rayon_core::thread_pool::ThreadPool::join::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/thread_pool/mod.rs:280:25
  44: rayon_core::thread_pool::ThreadPool::install::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/thread_pool/mod.rs:147:40
  45: rayon_core::registry::Registry::in_worker_cold::{{closure}}::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:522:21
  46: rayon_core::job::JobResult<T>::call::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:218:41
  47: <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/core/src/panic/unwind_safe.rs:272:9
  48: std::panicking::try::do_call
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/std/src/panicking.rs:559:40
  49: ___rust_try
  50: std::panicking::try
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/std/src/panicking.rs:523:19
  51: std::panic::catch_unwind
             at /rustc/032af18af578f4283a2927fb43b90df2bbb72b67/library/std/src/panic.rs:149:14
  52: rayon_core::unwind::halt_unwinding
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/unwind.rs:17:5
  53: rayon_core::job::JobResult<T>::call
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:218:15
  54: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:120:32
  55: rayon_core::job::JobRef::execute
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/job.rs:64:9
  56: rayon_core::registry::WorkerThread::execute
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:860:9
  57: rayon_core::registry::WorkerThread::wait_until_cold
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:794:21
  58: rayon_core::registry::WorkerThread::wait_until
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:769:13
  59: rayon_core::registry::WorkerThread::wait_until_out_of_work
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:818:9
  60: rayon_core::registry::main_loop
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:923:5
  61: rayon_core::registry::ThreadBuilder::run
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:53:18
  62: <rayon_core::registry::DefaultSpawn as rayon_core::registry::ThreadSpawn>::spawn::{{closure}}
             at /Users/nxs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rayon-core-1.12.1/src/registry.rs:98:20
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
thread caused non-unwinding panic. aborting.