Rename concat_lst to concat_list (#8597)
Schema improvements (#8286)
don't create duplicate pivot names (#8002)
rename toggle_string_cache to enable_string_cache (#7970)
change top_k(descending) -> bottom_k (#7969)
in sort, top_k, sort_by, and arg_sort_by, raise if descending is a sequence and its length doesn't match the number of columns to sort by (#7957)

🚀 Performance improvements

elide function calls in AnyValue::eq (#8725)
add fused multiply add optimization for expressions (#8690)
use expression for dot product (#8686)
improve nested grouptuples related code (#8618)
buffer spill partitions in ooc sort. ~10/20% (#8616)
improve OOC sort performance during partition phase (#8590)
remove some unnecessary calls and matches (#8490)
less naive count (#8473)
parallelize almost all flattens (#8468)
optimize horizontal min/max (#8463)
reinstate old behavior in numeric group-tuples (#8445)
remove false sharing in perfect hash table >2x (#8432)
further optimised conversions to python date/datetime (#8417)
optimize join inner materialization of single keys (#8405)
parallelize sorted group tuple materialization (#8387)
improve materialization of huge cardinality group tuples (#8382)
improve group_tuples materialization (#8375)
use online variance kernel for aggregation (#8306)
add specialized boolean aggregation for min/max (#8294)
fail fast on non-inferable strings in strptime if no fmt is provided (#8111)
make chunks search more resilient (#8229)
SIMD accelerated arg_min/arg_max (via argminmax) (#8074)
speed up csv parsing for slower datetimes formats (#8213)
arr.eval run on groupby expression engine when possible (#8199)
FromParalleIter<Option<str>> for Utf8Chunked ~1.9x (#8058)
speed up from_par_iter Option<bool> ~2.5x (#8057)
parallelize numeric ChunkedArray materialization ~2x. (#8053)
parallelize into_groups materialization ~-25% (#8036)
use a trusted anyvalue builder (#8001)
numeric grouptuples with nulls hash in single pass ~25% (#7980)
use perfect hash table for categoricals (#7951)
improve group_tuples of high cardinality data ~10% (#7938)
use streaming instead of partitioned groupby (#7907)
don't auto-stream groupby (#7906)
rechunk before aggs (#7903)
don't re-allocate groups in sorted to_dummies (#7897)

✨ Enhancements

add support for DISTINCT keyword in SQL select clauses (#8740)
support any day of the week in 'start_by' in groupby_dynamic (#8720)
add support for USING clause in SQL join operations (#8731)
add support for HAVING clause to SQL GROUP BY operations (#8704)
streaming unions (#8676)
expression cache (#8674)
rolling covariance and correlation (#8671)
Add dt.to_string alias for dt.strftime (#8290)
use temp dir for ooc spills (#8614)
make ooc-sort resilient against chunk_size (#8588)
Set strptime default strict/exact=true (#8587)
Out-of-core unique (#8573)
Add to_date, to_datetime, to_time to String namespace (#8579)
more detailed error message on failure to cast List dtype (#8583)
don't trigger unreachable code if no dtype is set (#8532)
accept expressions in groupby_dynamic/rolling (#8528)
expose quantile/mean for duration (#8491)
require explicitly sorted flag for upsample (#8488)
allow for _saturating suffix in duration strings (#8479)
let duration string accept "1mo_saturating" (#8469)
add dt.month_start and dt.month_end (#8435)
add SQL support for cumulative functions (#8457)
add str_slice method to StringNameSpace (#8427)
allow negative 'arange' expression (#8413)
warn if argument is not explicitly sorted (#8409)
Schema improvements (#8286)
add support for SQL "IN" expr (#8396)
cli output mode & sql read_json (#8336)
rename 'csv-file' to 'csv' (#8101)
preserve time zone in combine (#8263)
add use_earliest argument to replace_time_zone for dealing with ambiguous datetimes (#8087)
SQL CTE's (#8208)
add duration cumsum and remainder (#8219)
better algorithm for streaming unique (#8003)
Add approx distinct count via approx_unique() (#7937)
adopt FunctionExpr for cat namespace (#8173)
DatetimeArgs ergonomics (#8133)
Remove Seek constraint from IpcStreamReader and SerReader (#8166)
implement FunctionExpr for bound and round methods (#8172)
display skipped row if same number of rows (#8170)
move all boolean expressions into BooleanFunction enum (#8132)
rewrite log expressions to make them serializable (#8126)
make unique expr serde and cmp (#8153)
adopt FunctionExpr for abs to allow for serialization (#8129)
adopt FunctionExpr for cum* functions (#8130)
support negative index in pct_change (#8137)
add log1p to list of mathematical functions (#8102)
expand list of tz-aware formats which can be auto-inferred (#8085)
clearer error message if strptime without a fmt specified fails (#8086)
infer tz-aware formats with try_parse_dates in read_csv (#8084)
feat(python, rust)! make 'mo' interval raise if the target date does not exist (#8078)
auto-infer fmt for tz-aware date strings (#7405)
multiple sql contexts & optional sql highlighting in cli (#8072)
implement arg_sort for struct dtype (#8051)
support struct in df.unique (#7976)
change top_k(descending) -> bottom_k (#7969)
optimize away nested unions in lp (#7861)
Add seed argument to rank for random (#7913)
auto-infer detecting time-zone-awareness of fmt argument in strptime; deprecate tz_aware argument (#7886)
deal with null values in cut/qcut (#7878)
support datetime/date subclasses (e.g. FreezeGun) (#7819)

🐞 Bug fixes

groupby_dynamic was unnecessarily failing on ambiguous local datetime (#8737)
ensure count aggregation has proper length when spilling (#8735)
fix return value of std for single-element sequence with ddof=1 (#8730)
don't take logical plan during streaming fmt (#8711)
Don't upcast in round() for f32 when decimal is 0 (#8706)
block predicate containing shifts and windows after sort (#8670)
ensure perfect hash table processes the nulls (#8668)
Reading more tiny CSVs than workers in parallel will deadlock (#8441)
respect maintain_order in partitioned groupby (#8653)
fix explode null series (#8654)
fix categorical agg type (#8645)
allow list<null> -> list<cat> (#8636)
maintain sorted info on top-k and empty sort (#8615)
maintain sortedness in date -> datetime cast (#8606)
fix determining of supertype for tz-aware and tz-naive datetimes (#8585)
fix csv reader with new line in header (#8580)
correct for nested offsets in json serialization (#8584)
fix wrong dtype init in streaming groupby (#8574)
fix categorical/string_cache fill_null panic (#8562)
fix window function contention in binary expression (#8544)
fix StructChunked not_equal comparator/operator (#8547)
fix struct pyarrow ffi (#8543)
don't trigger unreachable code if no dtype is set (#8532)
keep sorted info on agg_first and simple singleton… (#8526)
unset fast_unique coming from arrow (#8521)
correct sign-reversed scale on DecimalChunked to Python Decimal conversion (fixes #8423) (#8508)
don't error on cast if column is not projected (#8495)
ensure window function succeeds on empty frame (#8492)
don't set verbose on union (#8487)
check literal/group length before claiming agg sta… (#8486)
fix error message of offset_by if offsetting by negative number of months (#8464)
fix sorted warning (#8462)
fix features serde and dtype-struct not compiling together (#8439)
respect dtype in anonymous list builder in case of… (#8428)
infer supertype in json serde (#8411)
duration on empty df (#8403)
don't inadvertently set Series initialised with nested tuple data as Object dtype (#8401)
use physical in streaming unique global table (#8390)
recursively bubble up all dtypes in list cast (#8386)
is_in struct logical types (#8378)
fix nested null parquet read (#8372)
fix logical type in ListChunked::new_from_index (#8367)
bubble up logical type in recursive list cast (#8356)
implement clone_inner for all series (#8357)
fix fill_null for categorical (#8353)
time.cast(str) as strftime (#8351)
fix logical dtypes in parallel list collection (#8349)
improve logical types of explode operation (#8348)
logical type in anonymous list builders (#8346)
escape csv header names if they contain special chars (#8331)
nested struct/list/categorical logical/physical (#8334)
fix deserialize empty list (#8326)
fix coalesce schema (#8324)
don't do null propagation (#8322)
ensure invalid list eval raises (#8317)
pass name to struct construction in aggregation (#8299)
Use three slashes for doc comments (#8284)
improve nested list construction (#8278)
Fix DataFrame.sum returning empty column names (#8283)
always sort in top_k fast path (#8275)
don't use fast paths for sorted join if there are … (#8272)
fix boolean par materialization (#8257)
improve null/empty list construction (#8255)
fix offsets in parallel utf8 materialization (#8254)
nested struct logical type consistency (#8249)
keep literal state if elementwise function is applied (#8195)
decimal ensure backed arrow arrays have correct dtype (#8193)
ensure cached nodes are initialized once (#8103)
validate map lenghts (#8147)
fix row-wise init of UInt64 values that exceed Int64 upper bound (#8146)
implement list<null> constructor (#8143)
add all primitives to av_buffer builder (#8140)
struct is_in (#8139)
fix wrong display name of binary expressions (#8131)
lazy: fix boolean sum schema (#8108)
don't exponentially grow error messages (partial fix). (#8081)
check element count in multi-column explode (#8050)
set lower limit for chunk_size (#8048)
impl to_static for struct (#8037)
all/any empty sets (#8012)
struct null_count, cast string, tranpose and describe (#8009)
fix pivot and transpose of struct data (#8005)
don't create duplicate pivot names (#8002)
fix chunked literals in expression engine (#7973)
in sort, top_k, sort_by, and arg_sort_by, raise if descending is a sequence and its length doesn't match the number of columns to sort by (#7957)
concat object types (#7958)
fix decimal conversion alignment (#7954)
Fix lazy encode schema (#7912)
respect skip_nulls in apply for temporal types (#7908)
fix lit agg (#7904)
disable ooc groupby (#7901)
fix abs logical type (#7895)
fix boolean min/max output type and null handling (#7894)
validate groupby_dynamic inputs (#7876)
correct for chunks in arg_where (#7873)
fix nested logical/physical list (#7872)
fix arbitrary nested logical types (#7869)
don't use fxhash in sink_sorted fast path (#7849)
parquet stats & all kernel (#7846)

🛠️ Other improvements

remove unnecessary feature flag requirement for start_by=monday in groupby_dynamic (#8716)
remove some branches (#8688)
streaming pipeline creation (#8656)
simplify replace_time_zone (#8644)
make slice attribute in UnionOptions consistent with … (#8639)
document the dispatcher (#8637)
Rename concat_lst to concat_list (#8597)
remove unreachable/duplicated code in get_supertype (#8592)
change partition strategy (#8561)
remove some unnecessary calls and matches (#8490)
improve sorted warning/ fix tests (#8484)
bubble up time_iter errors (#8467)
Minor update to strptime (#8345)
use concat_owned_array_unchecked when possible (#8274)
Rename strptime/strftime args (#8221)
change sampling ratio for groupby strategy (#8223)
Rename Expr.list to implode (#8165)
introduce FieldsMapper utility class for obtaining FunctionExpr schema (#8175)
don't panic on err in offset_by (#8210)
remove unused list_construction (#8197)
split dsl paragraph header (#8162)
feature flag guards (#8117)
use map_private where applicable to reduce code duplication (#8128)
remove unnecessary to_string (#8083)
docs(rust) Add note about -1 to show all rows. (#8080)
Fixed a bunch of clippy warnings (#7967)
rename toggle_string_cache to enable_string_cache (#7970)
Include license files in polars-error and polars-row crates (#7930)
quantile typo in qcut (#7936)
Improve Duration::parse docs (#7918)
improve shift and fill performance in case of periods >= ca.len() (#7843)

Thank you to all our contributors for making this release possible! @DeflateAwning, @JoonHong-Kim, @LdRoW, @MarcoGorelli, @Newtoniano, @StefanBRas, @alexander-beedie, @alonme, @ankane, @avimallu, @ayemjay, @borchero, @cgevans, @chitralverma, @clickingbuttons, @dependabot, @dependabot[bot], @ghuls, @grantmcdermott, @jonashaag, @josh, @jvdd, @lorentzenchr, @mcrumiller, @mzjp2, @n8henrie, @pgimalac, @rben01, @ritchie46, @stinodego, @uchiiii, @universalmind303, @utkarshgupta137, @zaynetro and @zundertj