Ben Kietzman created ARROW-11174:
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Summary: [C++][Dataset] Make Expressions available for projection
Key: ARROW-11174
URL: https://issues.apache.org/jira/browse/ARROW-11174
Project: Apache Arrow
Issue Type: Bug
Components: C++
Affects Versions: 2.0.0
Reporter: Ben Kietzman
Assignee: Ben Kietzman
Fix For: 4.0.0
RecordBatchProjector should be replaced by an expression calling the "project"
compute function.
Projection currently supports only reordering and subselection of fields,
materializing virtual columns where necessary. Replacement with an Expression
will enable specifying arbitrary expressions for projected columns:
{code:java}
// project an explicit selection:
// SELECT a as "a", b as "b" ...
project({field_ref("a"), field_ref("b")}, {"a", "b"});
// project an arithmetic expression:
// SELECT a + b as "a + b" ...
project({add(field_ref("a"), field_ref("b"))}, {"a + b"}){code}
This will also allow the same expression optimization machinery used for
filters to be directly applied to projections. Virtual columns become a
consequence of constant folding:
{code:java}
// project in a partition where a == 3:
assert(
SimplifyWithGuarantee(
project({field_ref("a"), field_ref("b")}, {"a", "b"}),
equal(field_ref("a"), literal(3))
)
== project({literal(3), field_ref("b")}, {"a", "b"})
){code}
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