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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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35 changes: 35 additions & 0 deletions arrow/src/record_batch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -244,6 +244,18 @@ impl RecordBatch {
&self.columns[..]
}

/// Return a new RecordBatch where each column is sliced
/// according to `offset` and `length`
pub fn slice(&self, offset: usize, length: usize) -> Result<RecordBatch> {
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can you remove the Result wrapping if nothing can fail.

let schema = self.schema();
let num_columns = self.num_columns();
let new_columns = (0..num_columns)
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self.columns().iter() ^_^

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My local version is

    /// Slice all the arrays in the record batch.
    pub fn slice(&self, offset: usize, len: usize) -> Self {
        let columns = self
            .columns()
            .iter()
            .map(|array| array.slice(offset, len))
            .collect();
        Self {
            schema: self.schema.clone(),
            columns,
        }
    }

Does it make sense to go through RecordBatch::try_new()? It incurs some overhead checking that the schema and arrays match, when they already should match

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@jorgecarleitao thanks, I have modified, PTAL

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@nevi-me Thanks for your suggestion, I made a modification. PTAL

.map(|column_index| self.column(column_index).slice(offset, length))
.collect();

RecordBatch::try_new(schema, new_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 @@ -426,6 +438,29 @@ mod tests {
assert_eq!(5, record_batch.column(1).data().len());
}

#[test]
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).unwrap();

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

#[test]
fn create_record_batch_try_from_iter() {
let a: ArrayRef = Arc::new(Int32Array::from(vec![
Expand Down