🏆 Highlights

• Full plan CSE (#15264)

💥 Breaking changes

• rename memmap -> memory_map as like Python (#15642)
• pref(rust!, python): Unify sort with SortOptions and SortMultipleOptions (#15590)
• Update the argument name from dims to dimensions in reshape (#15561)
• Allow specifying Hive schema in read/scan_parquet (#15434)
• Raise error when schema_overrides contains nonexistent column name (#15290)
• Rename Chunk to RecordBatch (#15298)
• Refactor AnyValue supertype logic (#15280)
• Rename group_by_rolling to rolling and improve related error messages (#14765)
• Rename ChunkedArray.try_apply to try_apply_values (#14947)
• Rename parameter by to group_by in DataFrame.upsample/group_by_dynamic/rolling (#14840)

🚀 Performance improvements

• Fix cross join batch size when one of the DataFrames is tiny (#14347)
• Fix binview growable complexity O(n*m) -> O(n) (#15628)
• Remove extra thread spawn from row group fetcher (#15626)
• Use vertical parallelism if input is chunked for Filter,Select,WithColumns (#15608)
• read_ipc memory usage tests, and writing fix (#15599)
• Refactor CSV serialization to not go thorough AnyValue (#15576)
• don't use dynamic dispatch in visitors (#15607)
• Improve Bitmap construction performance (#15570)
• join by row-encoding (#15559)
• Replace std::thread spawn with tokio block_in_place (#15517)
• speed up offset_by when a single offset is passed (#15493)
• Avoid allocation in the hot path for struct JSON serialization (#15449)
• avoid double-allocation in rolling_apply_agg_window (#15423)
• Make LogicalPlan immutable (#15416)
• Add non-order preserving variable row-encoding (#15414)
• Use row-encoding for multiple key group by (#15392)
• load bits one word at a time for BitmapIter (#15333)
• Ipc exec multiple paths (#15040)
• add SIMD support for if-then-else kernels (#15131)

✨ Enhancements

• add Expr.dt.add_business_days and Series.dt.add_business_days (#15595)
• Add str.head and str.tail (#14425)
• Extended BytecodeParser to handle additional math functions, and imports from the global namespace (#15627)
• Push down is_between expressions to Arrow (#15180)
• add holidays argument to business_day_count (#15580)
• change default to write parquet statistics (#15597)
• Expressify to_integer (#15604)
• Optimizer; remove double SORT and redundant projections (#15573)
• Add null_on_oob parameter to expr.array.get (#15426)
• support weekend argument in business_day_count (#15544)
• Enable is_first/last_distinct for not nested non-numeric list (#15552)
• Turn off cse if cache node found (#15554)
• Tag concat list as elementwise (#15545)
• Support list group-by of non numeric lists (#15540)
• add business_day_count function (#15512)
• Add SQL support for MEDIAN aggfunc (#15519)
• Implement string, boolean and binary dtype in top_k (#15488)
• Add SQL support for TRUNCATE TABLE command (#15513)
• Add SQL support for GREATEST and LEAST (#15511)
• Allow specifying Hive schema in read/scan_parquet (#15434)
• Implements agg_list for NullChunked (#15439)
• Supports explode_by_offsets for decimal (#15417)
• Add null_on_oob parameter to expr.list.get (#15395)
• CSV-writer escape carriage return (#15399)
• Remove 'FileCacher' optimization (#15357)
• check input type in entropy (#15351)
• Implements arr.n_unique (#15296)
• CSE don't scan share if predicate pushdown predicates don't match (#15328)
• Remove cached nodes when finished (#15310)
• Full plan CSE (#15264)
• Add IR for expressions. (#15168)
• Warn if map_elements is called without return_dtype specified (#15188)
• Rename group_by_rolling to rolling and improve related error messages (#14765)
• Rename ChunkedArray.try_apply to try_apply_values (#14947)
• Implement strict AnyValue construction for temporal types (#15146)

🐞 Bug fixes

• Return appropriate data type for time mean and median (#14471)
• Support index upsampling (#13621)
• Fix issue in write_excel that could lead to incorrect spanning range determination (#15631)
• Output correct dtype for mean_horizontal on a single column (#15118)
• Recompute RowIndex schema after projection pd (#15625)
• Mean of boolean in streaming group_by incorrectly always gave NULL (#15616)
• Include cloud creds in cache key (#15609)
• Fix elementwise-apply if any input is AggregatedScalar (#15606)
• Explode list should take validity into account (#15572)
• use larger recursive stack in debug mode (#15593)
• SQL interface "off-by-one' indexing error with GROUP BY clauses that use position ordinals (#15584)
• Enable missing features in polars-time (#15558)
• Handle quoted identifiers when registering CTEs in the SQL engine (#15564)
• Decompress moved out of schema initialization (#15550)
• Turn off cse if cache node found (#15554)
• Resolve function names and prune all aliases. (#15522)
• list.get should take validity into account (#15516)
• block decimal in streaming (#15520)
• group_by partitioned with literal Series panic (#15487)
• Initialize validity for GroupsProxy::Slice windows (#15509)
• Fix struct name resolving (#15507)
• pow return type evaluation (#15506)
• Allow selectors inside frame-level .filter() (#15445)
• Don't prune alias in AnonymousFunction subtree (#15453)
• Fix deadlock in async parquet scan (#15440)
• datetime operations (e.g. .dt.year) were raising when null values were backed by out-of-range integers (#15420)
• Ensure Binary -> Binview cast doesn't overflow the buffer size (#15408)
• Don't prune alias in function subtree (#15406)
• Return 0 for n_unique() in group-by context when group is empty (#15289)
• Unset UpdateGroups after group-sensitive expression (#15400)
• to_any_value should supports all LiteralValue type (#15387)
• Hash failure combining hash of two numeric columns containing equal values (#15397)
• Add FixedSizeBinary to arrow field conversion (#15389)
• Conversion of expr_ir in partition fast path (#15388)
• sort for series with unsupported dtype should raise instead of panic (#15385)
• Return correct dtype for s.clear() when dtype is Object (#15315)
• ensure first datapoint is always included in group_by_dynamic (#15312)
• Non-exhaustive patterns: arrow-schema::DataType in polars-arrow (#15250)
• use dynamic stacks for problematic recursive functions (#15355)
• Raise error when schema_overrides contains nonexistent column name (#15290)
• Fix cache dot visualization (#15311)
• Properly propagate strict flag when constructing a Struct Series from any values (#15302)
• ensure eq for BinaryViewArray checks all elements (#15268)
• Raise when join projects name with suffix that doesn't exist (#15256)
• fix kurtosis/skew (#15137)
• Ensure ooc_start is set (#15255)
• Fix bug where rolling operations were ignoring check_sorted in some cases (#15227)
• Fix lazy schema for rle expression (#15248)
• incorrect negative offset in multi-byte string slicing (#15140)
• do not clamp negative offsets to start of array prematurely (#15242)
• allow null index in list.get and array.get (#15239)
• properly support nulls_last + descending (#15212)
• Block rounding/truncating to negative durations (#15175)
• Make parse_url work on windows with object_store (#15191)
• divide by zero in download speed computation (#15182)

📖 Documentation

• Add legacy CPU install instructions in user guide (#13676)
• Various minor updates to User Guide's SQL intro section (#15557)
• Add outer_coalesce join strategy in the user guide (#15405)
• Improve docs for Series::new with AnyValue input (#15306)
• Fix formatting in Series::from_any_values_and_dtype docs (#15244)
• Correct the definition of an expression in the user guide (#14750)

📦 Build system

• Fix a feature gate for lz4 compression in polars-parquet (#15565)
• Update Rust toolchain (#15353)

🛠️ Other improvements

• rename memmap -> memory_map as like Python (#15642)
• fixup failing test due to offset deprecation in upsample (#15636)
• use bound api (#15630)
• Don't run streaming group-by in partitionable gb (#15611)
• pref(rust!, python): Unify sort with SortOptions and SortMultipleOptions (#15590)
• remove try_binary_elementwise_values (#15592)
• remove raw pointers from visitors. (#15579)
• rename to IR (#15571)
• Update the argument name from dims to dimensions in reshape (#15561)
• Rename ALogicalPlan to FullAccessIR (#15553)
• Set up CodSpeed (#15537)
• make dsl immutable and cheap to clone (#15394)
• use recursive crate, add missing recursive tag (#15393)
• Update CODEOWNERS (polars-sql) (#15384)
• Update Rust toolchain (#15353)
• Update CODEOWNERS (#15352)
• remove try_apply_values (#15336)
• always use non-legacy float_sum for mean (#15343)
• remove legacy bitmap module (#15335)
• More clippy in Makefile (#15340)
• Rename Cache[count] to Cache[cache_hits] (#15300)
• Cleanup file_caching optimization call (#15299)
• Rename Chunk to RecordBatch (#15298)
• Refactor AnyValue supertype logic (#15280)
• reuse message parsing in IPC (#15265)
• remove 'fast-projection' node (#15253)
• cleanup column names in optimizer (#15252)
• remove left_most_input_name from expr ir (#15251)
• add AlignedBitmapSlice (#15171)
• Refactor AnyValue construction for Categorical/Enum dtype (#15220)
• Move ConsecutiveCountState into support module (#15186)
• Run non-benchmark tests in benchmark workflow (#15207)
• Add wrapping_abs to arithmetic kernel (#15210)
• remove raw buffers from BinViewArray (#15206)
• Enable RUST_BACKTRACE=1 in the CI test suite (#15204)
• Rename parameter by to group_by in DataFrame.upsample/group_by_dynamic/rolling (#14840)
• Set dual license for polars-arrow and polars-parquet (#15173)
• remove parts of legacy bit_util (#15169)
• remove legacy arrow compute (#15164)

Thank you to all our contributors for making this release possible! @CanglongCl, @ChayimFriedman2, @Fokko, @JamesCE2001, @MarcoGorelli, @NedJWestern, @Sol-Hee, @TrevorWinstral, @alexander-beedie, @braaannigan, @c-peters, @cmdlineluser, @cojmeister, @deanm0000, @dependabot, @dependabot[bot], @douglas-raillard-arm, @eitsupi, @filabrazilska, @henryharbeck, @i-aki-y, @itamarst, @kszlim, @leoforney, @mbuhidar, @mcrumiller, @mickvangelderen, @nameexhaustion, @orlp, @ozgrakkurt, @petrosbar, @reswqa, @ritchie46, @rob-sil, @sportfloh, @stinodego, @thomaslin2020 and @yutannihilation