[Python][Gandiva] Offset is ignored in Gandiva projector #4420
Description
I used the test case in https://github.com/apache/arrow/blob/master/python/pyarrow/tests/test_gandiva.py#L25, and found an issue when I was using the slice operator input_batch[1:]. It seems that the offset is ignored in the Gandiva projector.
import pyarrow as pa
import pyarrow.gandiva as gandiva
builder = gandiva.TreeExprBuilder()
field_a = pa.field('a', pa.int32())
field_b = pa.field('b', pa.int32())
schema = pa.schema([field_a, field_b])
field_result = pa.field('res', pa.int32())
node_a = builder.make_field(field_a)
node_b = builder.make_field(field_b)
condition = builder.make_function("greater_than", [node_a, node_b],
pa.bool_())
if_node = builder.make_if(condition, node_a, node_b, pa.int32())
expr = builder.make_expression(if_node, field_result)
projector = gandiva.make_projector(
schema, [expr], pa.default_memory_pool())
a = pa.array([10, 12, -20, 5], type=pa.int32())
b = pa.array([5, 15, 15, 17], type=pa.int32())
e = pa.array([10, 15, 15, 17], type=pa.int32())
input_batch = pa.RecordBatch.from_arrays([a, b], names=['a', 'b'])
r, = projector.evaluate(input_batch[1:])
print(r)If we use the full record batch input_batch, the expected output is [10, 15, 15, 17]. So if we use input_batch[1:], the expected output should be [15, 15, 17], however this script returned [10, 15, 15]. It seems that the projector ignores the offset and always reads from 0.