feat: expose lambda and higher-order array functions#1561
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Add a Pythonic API for DataFusion's higher-order array functions and the lambda expressions they consume. - Rust: lambda_, lambda_var, array_transform, and array_any_match pyfunctions, plus a ResolveLambdaVariables analyzer rule so expression-builder plans (which emit unresolved lambda variables) resolve before optimization. - Python: array_transform / array_any_match (with list_transform, any_match, list_any_match aliases) accept either a Python callable or an explicit lambda built with lambda_ / lambda_var. Callables are introspected so their parameter names become the lambda parameters. - Tests and docs (expressions guide + agent skill), noting v1 limits: lambda expressions are not serializable, and SQL arrow syntax needs the DuckDB dialect.
Combine the eight higher-order function result tests into a single parametrized test_higher_order_function_results, and the two to_lambda rejection tests into test_to_lambda_rejects_invalid_arg. Each case keeps a readable id via pytest.param. Co-Authored-By: Claude <noreply@anthropic.com>
Add array_filter, the remaining lambda-based higher-order array function in DataFusion (alongside the already-exposed array_transform and array_any_match). Includes the list_filter alias matching upstream, tests, and documentation in the expressions guide and skill. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Lead user-facing array-lambda docs with "lambda function" instead of "higher-order function," which is less recognizable to users. Drop the alias list, serialization caveat, and DuckDB-dialect note from the skill to keep it lean; those details already live in the docstrings. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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gstvg
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| contains a lambda raises ``Lambda not implemented``. SQL lambda syntax | ||
| (``x -> x * 2``) is only parsed by dialects that support lambdas; set | ||
| ``datafusion.sql_parser.dialect`` to ``DuckDB`` to use it. The Python |
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DuckDB will remove this syntax in v2.1. Perhaps add other dialects that support this syntax (spark, databricks, clickhouse, snowflake), and/or add the new duckdb syntax (``lambda x: x *2`) ?
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Which issue does this PR close?
Closes #811
Rationale for this change
DataFusion gained lambda expressions and higher-order array functions (apache/datafusion#21172). The Python binding already had the read-only
Lambda,HigherOrderFunction, andLambdaVariablewrapper classes, but offered no way to construct a lambda or call the higher-order functions. This PR adds a Pythonic API for both.What changes are included in this PR?
Adds the following:
array_transformandarray_any_matchthat accept either a Python callable or an explicit lambda built withlambda_/lambda_varAre there any user-facing changes?
There are new APIs but they are all new additions.