Add the LINQ operators Query.jl is missing

[davidanthoff]

Query.jl's operator set has been frozen roughly at the .NET Framework 3.5 System.Linq.Enumerable surface. This adds the 38 operators it is missing — both the ones .NET has added since (.NET 6 through 11) and older ones that were never ported.

This is the first of four PRs, one per package in the stack. Query.jl (macros + docs), QueryableBackend.jl (Queryable nodes) and QueryDuckDB.jl (SQL push-down) follow once this is registered.

Operators added

Commit	Operators	.NET origin
Outer joins	left_join, right_join, full_join	.NET 11
Set operations	concat, union, union_by, except, except_by, intersect, intersect_by	*By are .NET 6
Ordering	order, order_descending, reverse, shuffle, index	.NET 7 / 10 / 9
Keyed aggregation	count_by, aggregate_by, chunk	.NET 9 / 9 / 6
Partitioning	take_while, drop_while, take_last, drop_last	—
Combining	append, prepend, zip	—
Terminal	min_by, max_by, any, all, contains, sequence_equal, aggregate, first, last, single, element_at	MinBy/MaxBy are .NET 6
Type filtering	of_type, cast	—

One commit per group, so the PR can be reviewed group by group. Sequence, InfiniteSequence, Range, Repeat, Empty, TryGetNonEnumeratedCount and the To* collectors are deliberately skipped — Julia ranges, Iterators.repeated and Query's sinks already cover them. DistinctBy is already unique(f).

Following the convention here, no macros were added to operators.jl — the existing ones are legacy, consumed only by Query/src/query_translation.jl's @from path and this package's own tests, and the three most recent operators (pivot_longer, pivot_wider, summarize) have bare function … end declarations. The user-facing macros will land in the Query.jl PR.

Points worth a look

Nullability is DataValue, never Missing. The unmatched side of an outer join is built by a new _default_value, a generated runtime counterpart of the existing _default_value_expr. Matched elements on a nullable side are converted to the same all-null-capable type, so a single element type covers matched and unmatched rows — the trick EnumerableDefaultIfEmpty already uses. Tests assert the result is DataValue and carries no missing.

except_by/intersect_by deviate from .NET. Enumerable.ExceptBy and IntersectBy take a bare sequence of keys as their second argument, while UnionBy takes a sequence of elements. Here the key selector is applied to both sequences in all three cases. That keeps the three consistent with each other, matches the shape of the equivalent SQL (WHERE k NOT IN (SELECT k FROM b)), and is what a table-shaped second argument makes natural. Happy to switch to strict .NET parity if you'd rather.

index and element_at are 1-based, matching Julia rather than .NET's 0-based Index()/ElementAt.

count_by/aggregate_by name their key columns through the existing _key_namedtuple, so they agree with summarize: a scalar key becomes a column called key, a NamedTuple key contributes one column per field. A test asserts count_by and groupby-plus-summarize produce identical output. summarize remains the idiomatic way to aggregate; aggregate_by is here for LINQ parity.

Defining any in this module captured the Base.any call in enumerable_pivot.jl, which is now qualified. A test covers that regression. union, intersect, reverse, zip, append, first, last, any, all, contains shadow Base, as map, filter, count, take, unique and join already do here; that one call site was the only casualty.

Random is a new dependency, for shuffle. It takes an optional RNG, which makes it reproducible.

Laziness

concat, union, take_while, drop_while, drop_last, append, prepend, zip, index, of_type and cast are lazy, with tests asserting sources are not over-read (e.g. zip pulls at most one element past the end of the shorter source, chunk only walks as far as the batches consumed). reverse, shuffle, order and the keyed aggregations have to collect first.

Testing

134 test items pass, 96 of them new. Each operator covers empty sources, empty second sequences, duplicate keys, out-of-range counts, eltype, IteratorSize/length, and a case applied downstream of @groupby so Grouping elements are exercised.

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