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Implement function slice for RecordBatch #490

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merged 5 commits into from
Jun 25, 2021
Merged

Implement function slice for RecordBatch #490

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523d426
Implement RecordBatch::slice()
b41sh Jun 22, 2021
738dd26
optimize
b41sh Jun 22, 2021
856d8c4
optimize
b41sh Jun 22, 2021
34f7194
add test case
b41sh Jun 24, 2021
9aacab1
fix clippy
b41sh Jun 24, 2021
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91 changes: 84 additions & 7 deletions arrow/src/record_batch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -244,6 +244,31 @@ impl RecordBatch {
&self.columns[..]
}

/// Return a new RecordBatch where each column is sliced
/// according to `offset` and `length`
///
/// # Panics
///
/// Panics if `offset` with `length` is greater than column length.
pub fn slice(&self, offset: usize, length: usize) -> RecordBatch {
if self.schema.fields().len() == 0 {
assert!((offset + length) == 0);
return RecordBatch::new_empty(self.schema.clone());
}
assert!((offset + length) <= self.num_rows());

let columns = self
.columns()
.iter()
.map(|column| column.slice(offset, length))
.collect();

Self {
schema: self.schema.clone(),
columns,
}
}

/// Create a `RecordBatch` from an iterable list of pairs of the
/// form `(field_name, array)`, with the same requirements on
/// fields and arrays as [`RecordBatch::try_new`]. This method is
Expand Down Expand Up @@ -414,16 +439,68 @@ mod tests {
let record_batch =
RecordBatch::try_new(Arc::new(schema), vec![Arc::new(a), Arc::new(b)])
.unwrap();
check_batch(record_batch)
check_batch(record_batch, 5)
}

fn check_batch(record_batch: RecordBatch) {
assert_eq!(5, record_batch.num_rows());
fn check_batch(record_batch: RecordBatch, num_rows: usize) {
assert_eq!(num_rows, record_batch.num_rows());
assert_eq!(2, record_batch.num_columns());
assert_eq!(&DataType::Int32, record_batch.schema().field(0).data_type());
assert_eq!(&DataType::Utf8, record_batch.schema().field(1).data_type());
assert_eq!(5, record_batch.column(0).data().len());
assert_eq!(5, record_batch.column(1).data().len());
assert_eq!(num_rows, record_batch.column(0).data().len());
assert_eq!(num_rows, record_batch.column(1).data().len());
}

#[test]
#[should_panic(expected = "assertion failed: (offset + length) <= self.num_rows()")]
fn create_record_batch_slice() {
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can you test for edge cases, e.g. empty length, over boundary offset, empty columns, empty batch, etc.

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@jimexist I have a question, if an empty RecordBatch calls slice(), the offset and length are zero, should we panic or return an empty RecordBatch slice?

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It should return an empty slice.

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It should return an empty slice.

ok

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I have modified, PTAL
@Dandandan @jimexist

let schema = Schema::new(vec![
Field::new("a", DataType::Int32, false),
Field::new("b", DataType::Utf8, false),
]);
let expected_schema = schema.clone();

let a = Int32Array::from(vec![1, 2, 3, 4, 5, 6, 7, 8]);
let b = StringArray::from(vec!["a", "b", "c", "d", "e", "f", "h", "i"]);

let record_batch =
RecordBatch::try_new(Arc::new(schema), vec![Arc::new(a), Arc::new(b)])
.unwrap();

let offset = 2;
let length = 5;
let record_batch_slice = record_batch.slice(offset, length);

assert_eq!(record_batch_slice.schema().as_ref(), &expected_schema);
check_batch(record_batch_slice, 5);

let offset = 2;
let length = 0;
let record_batch_slice = record_batch.slice(offset, length);

assert_eq!(record_batch_slice.schema().as_ref(), &expected_schema);
check_batch(record_batch_slice, 0);

let offset = 2;
let length = 10;
let _record_batch_slice = record_batch.slice(offset, length);
}

#[test]
#[should_panic(expected = "assertion failed: (offset + length) == 0")]
fn create_record_batch_slice_empty_batch() {
let schema = Schema::new(vec![]);

let record_batch = RecordBatch::new_empty(Arc::new(schema));

let offset = 0;
let length = 0;
let record_batch_slice = record_batch.slice(offset, length);
assert_eq!(0, record_batch_slice.schema().fields().len());

let offset = 1;
let length = 2;
let _record_batch_slice = record_batch.slice(offset, length);
}

#[test]
Expand All @@ -445,7 +522,7 @@ mod tests {
Field::new("b", DataType::Utf8, false),
]);
assert_eq!(record_batch.schema().as_ref(), &expected_schema);
check_batch(record_batch);
check_batch(record_batch, 5);
}

#[test]
Expand All @@ -465,7 +542,7 @@ mod tests {
Field::new("b", DataType::Utf8, true),
]);
assert_eq!(record_batch.schema().as_ref(), &expected_schema);
check_batch(record_batch);
check_batch(record_batch, 5);
}

#[test]
Expand Down