v21.06.00

🚨 Breaking Changes

• Add support for make_meta_obj dispatch in dask-cudf (#8342) @galipremsagar
• Add separator-on-null parameter to strings concatenate APIs (#8282) @davidwendt
• Introduce a common parent class for NumericalColumn and DecimalColumn (#8278) @vyasr
• Update ORC statistics API to use C++17 standard library (#8241) @vuule
• Preserve column hierarchy when getting NULL row from LIST column (#8206) @isVoid
• Groupby.shift c++ API refactor and python binding (#8131) @isVoid

🐛 Bug Fixes

• Fix struct flattening to add a validity column only when the input column has null element (#8374) @ttnghia
• Compilation fix: Remove redefinition for std::is_same_v() (#8369) @mythrocks
• Add backward compatibility for dask-cudf to work with other versions of dask (#8368) @galipremsagar
• Handle empty results with nested types in copy_if_else (#8359) @nvdbaranec
• Handle nested column types properly for empty parquet files. (#8350) @nvdbaranec
• Raise error when unsupported arguments are passed to dask_cudf.DataFrame.sort_values (#8349) @galipremsagar
• Raise NotImplementedError for axis=1 in rank (#8347) @galipremsagar
• Add support for make_meta_obj dispatch in dask-cudf (#8342) @galipremsagar
• Update Java string concatenate test for single column (#8330) @tgravescs
• Use empty_like in scatter (#8314) @revans2
• Fix concatenate_lists_ignore_null on rows of all_nulls (#8312) @sperlingxx
• Add separator-on-null parameter to strings concatenate APIs (#8282) @davidwendt
• COLLECT_LIST support returning empty output columns. (#8279) @mythrocks
• Update io util to convert path like object to string (#8275) @ayushdg
• Fix result column types for empty inputs to rolling window (#8274) @mythrocks
• Actually test equality in assert_groupby_results_equal (#8272) @shwina
• CMake always explicitly specify a source files extension (#8270) @robertmaynard
• Fix struct binary search and struct flattening (#8268) @ttnghia
• Revert "patch thrust to fix intmax num elements limitation in scan_by_key" (#8263) @cwharris
• upgrade dlpack to 0.5 (#8262) @cwharris
• Fixes CSV-reader type inference for thousands separator and decimal point (#8261) @elstehle
• Fix incorrect assertion in Java concat (#8258) @sperlingxx
• Copy nested types upon construction (#8244) @isVoid
• Preserve column hierarchy when getting NULL row from LIST column (#8206) @isVoid
• Clip decimal binary op precision at max precision (#8194) @ChrisJar

📖 Documentation

• Add docstring for dask_cudf.read_csv (#8355) @galipremsagar
• Fix cudf release version in readme (#8331) @galipremsagar
• Fix structs column description in dev docs (#8318) @isVoid
• Update readme with correct CUDA versions (#8315) @raydouglass
• Add description of the cuIO GDS integration (#8293) @vuule
• Remove unused parameter from copy_partition kernel documentation (#8283) @robertmaynard

🚀 New Features

• Add support merging b/w categorical data (#8332) @galipremsagar
• Java: Support struct scalar (#8327) @sperlingxx
• added _is_homogeneous property (#8299) @shaneding
• Added decimal writing for CSV writer (#8296) @kaatish
• Java: Support creating a scalar from utf8 string (#8294) @firestarman
• Add Java API for Concatenate strings with separator (#8289) @tgravescs
• strings::join_list_elements options for empty list inputs (#8285) @ttnghia
• Return python lists for getitem calls to list type series (#8265) @brandon-b-miller
• add unit tests for lead/lag on list for row window (#8259) @wbo4958
• Create a String column from UTF8 String byte arrays (#8257) @firestarman
• Support scattering list_scalar (#8256) @isVoid
• Implement lists::concatenate_list_elements (#8231) @ttnghia
• Support for struct scalars. (#8220) @nvdbaranec
• Add support for decimal types in ORC writer (#8198) @vuule
• Support create lists column from a list_scalar (#8185) @isVoid
• Groupby.shift c++ API refactor and python binding (#8131) @isVoid
• Add groupby::replace_nulls(replace_policy) api (#7118) @isVoid

🛠️ Improvements

• Support Dask + Distributed 2021.05.1 (#8392) @jakirkham
• Add aliases for string methods (#8353) @shwina
• Update environment variable used to determine cuda_version (#8321) @ajschmidt8
• JNI: Refactor the code of making column from scalar (#8310) @firestarman
• Update CHANGELOG.md links for calver (#8303) @ajschmidt8
• Merge branch-0.19 into branch-21.06 (#8302) @ajschmidt8
• use address and length for GDS reads/writes (#8301) @rongou
• Update cudfjni version to 21.06.0 (#8292) @pxLi
• Update docs build script (#8284) @ajschmidt8
• Make device_buffer streams explicit and enforce move construction (#8280) @harrism
• Introduce a common parent class for NumericalColumn and DecimalColumn (#8278) @vyasr
• Do not add nulls to the hash table when null_equality::NOT_EQUAL is passed to left_semi_join and left_anti_join (#8277) @nvdbaranec
• Enable implicit casting when concatenating mixed types (#8276) @ChrisJar
• Fix CMake FindPackage rmm, pin dev envs' dlpack to v0.3 (#8271) @trxcllnt
• Update cudfjni version to 21.06 (#8267) @pxLi
• support RMM aligned resource adapter in JNI (#8266) @rongou
• Pass compiler environment variables to conda python build (#8260) @Ethyling
• Remove abc inheritance from Serializable (#8254) @vyasr
• Move more methods into SingleColumnFrame (#8253) @vyasr
• Update ORC statistics API to use C++17 standard library (#8241) @vuule
• Correct unused parameter warnings in dictonary algorithms (#8239) @robertmaynard
• Correct unused parameters in the copying algorithms (#8232) @robertmaynard
• IO statistics cleanup (#8191) @kaatish
• Refactor of rolling_window implementation. (#8158) @nvdbaranec
• Add a flag for allowing single quotes in JSON strings. (#8144) @nvdbaranec
• Column refactoring 2 (#8130) @vyasr
• support space in workspace (#7956) @jolorunyomi
• Support collect_set on rolling window (#7881) @sperlingxx