Function evaluate_demo

datafusion-examples/examples/query_planning/expr_api.rs:128–155

DataFusion can also evaluate arbitrary expressions on Arrow arrays.

()

/// DataFusion can also evaluate arbitrary expressions on Arrow arrays.
fn evaluate_demo() -> Result<()> {
    // For example, let's say you have some integers in an array
    let batch = RecordBatch::try_from_iter([(
        "a",
        Arc::new(Int32Array::from(vec![4, 5, 6, 7, 8, 7, 4])) as _,
    )])?;

    // If you want to find all rows where the expression `a < 5 OR a = 8` is true
    let expr = col("a").lt(lit(5)).or(col("a").eq(lit(8)));

    // First, you make a "physical expression" from the logical `Expr`
    let df_schema = DFSchema::try_from(batch.schema())?;
    let physical_expr = SessionContext::new().create_physical_expr(expr, &df_schema)?;

    // Now, you can evaluate the expression against the RecordBatch
    let result = physical_expr.evaluate(&batch)?;

    // The result contain an array that is true only for where `a < 5 OR a = 8`
    let expected_result = Arc::new(BooleanArray::from(vec![
        true, false, false, false, true, false, true,
    ])) as _;
    assert!(
        matches!(&result, ColumnarValue::Array(r) if r == &expected_result),
        "result: {result:?}"
    );

    Ok(())
}

/// In addition to easy construction, DataFusion exposes APIs for simplifying
/// such expression so they are more efficient to evaluate. This code is also