arrow/examples/dynamic_types.rs

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// to you under the Apache License, Version 2.0 (the
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//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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///! This example demonstrates dealing with mixed types dynamically at runtime
use std::sync::Arc;

extern crate arrow;

use arrow::array::*;
use arrow::datatypes::*;
use arrow::error::Result;
use arrow::record_batch::*;

fn main() -> Result<()> {
    // define schema
    let schema = Schema::new(vec![
        Field::new("id", DataType::Int32, false),
        Field::new(
            "nested",
            DataType::Struct(vec![
                Field::new("a", DataType::Utf8, false),
                Field::new("b", DataType::Float64, false),
                Field::new("c", DataType::Float64, false),
            ]),
            false,
        ),
    ]);

    // create some data
    let id = Int32Array::from(vec![1, 2, 3, 4, 5]);

    let nested = StructArray::from(vec![
        (
            Field::new("a", DataType::Utf8, false),
            Arc::new(StringArray::from(vec!["a", "b", "c", "d", "e"])) as Arc<dyn Array>,
        ),
        (
            Field::new("b", DataType::Float64, false),
            Arc::new(Float64Array::from(vec![1.1, 2.2, 3.3, 4.4, 5.5])),
        ),
        (
            Field::new("c", DataType::Float64, false),
            Arc::new(Float64Array::from(vec![2.2, 3.3, 4.4, 5.5, 6.6])),
        ),
    ]);

    // build a record batch
    let batch =
        RecordBatch::try_new(Arc::new(schema), vec![Arc::new(id), Arc::new(nested)])?;

    process(&batch);
    Ok(())
}

/// Create a new batch by performing a projection of id, nested.c
fn process(batch: &RecordBatch) {
    let id = batch.column(0);
    let nested = batch
        .column(1)
        .as_any()
        .downcast_ref::<StructArray>()
        .unwrap();

    let _nested_b = nested
        .column(1)
        .as_any()
        .downcast_ref::<Float64Array>()
        .unwrap();
    let nested_c: &Float64Array = nested
        .column(2)
        .as_any()
        .downcast_ref::<Float64Array>()
        .unwrap();

    let projected_schema = Schema::new(vec![
        Field::new("id", DataType::Int32, false),
        Field::new("sum", DataType::Float64, false),
    ]);

    let _ = RecordBatch::try_new(
        Arc::new(projected_schema),
        vec![
            id.clone(), // NOTE: this is cloning the Arc not the array data
            Arc::new(Float64Array::from(nested_c.data().clone())),
        ],
    );
}