Expand description
A comparable row-oriented representation of a collection of Array
As Row
are normalized for sorting, they can be very efficiently compared,
using memcmp
under the hood, or used in non-comparison sorts such as radix sort. This
makes the row format ideal for implementing efficient multi-column sorting,
grouping, aggregation, windowing and more.
Comparing Rows
generated by different RowConverter
is not guaranteed to
yield a meaningful ordering
let a1 = Arc::new(Int32Array::from_iter_values([-1, -1, 0, 3, 3])) as ArrayRef;
let a2 = Arc::new(StringArray::from_iter_values(["a", "b", "c", "d", "d"])) as ArrayRef;
let arrays = vec![a1, a2];
// Convert arrays to rows
let mut converter = RowConverter::new(vec![
SortField::new(DataType::Int32),
SortField::new(DataType::Utf8),
]).unwrap();
let rows = converter.convert_columns(&arrays).unwrap();
// Compare rows
for i in 0..4 {
assert!(rows.row(i) <= rows.row(i + 1));
}
assert_eq!(rows.row(3), rows.row(4));
// Convert rows back to arrays
let converted = converter.convert_rows(&rows).unwrap();
assert_eq!(arrays, converted);
// Compare rows from different arrays
let a1 = Arc::new(Int32Array::from_iter_values([3, 4])) as ArrayRef;
let a2 = Arc::new(StringArray::from_iter_values(["e", "f"])) as ArrayRef;
let arrays = vec![a1, a2];
let rows2 = converter.convert_columns(&arrays).unwrap();
assert!(rows.row(4) < rows2.row(0));
assert!(rows.row(4) < rows2.row(1));
// Convert selection of rows back to arrays
let selection = [rows.row(0), rows2.row(1), rows.row(2), rows2.row(0)];
let converted = converter.convert_rows(selection).unwrap();
let c1 = as_primitive_array::<Int32Type>(converted[0].as_ref());
assert_eq!(c1.values(), &[-1, 4, 0, 3]);
let c2 = as_string_array(converted[1].as_ref());
let c2_values: Vec<_> = c2.iter().flatten().collect();
assert_eq!(&c2_values, &["a", "f", "c", "e"]);
It can also be used to implement a fast multi-column / lexicographic sort
fn lexsort_to_indices(arrays: &[ArrayRef]) -> UInt32Array {
let fields = arrays
.iter()
.map(|a| SortField::new(a.data_type().clone()))
.collect();
let mut converter = RowConverter::new(fields).unwrap();
let rows = converter.convert_columns(&arrays).unwrap();
let mut sort: Vec<_> = rows.iter().enumerate().collect();
sort.sort_unstable_by(|(_, a), (_, b)| a.cmp(b));
UInt32Array::from_iter_values(sort.iter().map(|(i, _)| *i as u32))
}
Structs
A comparable representation of a row
Converts
ArrayRef
columns into a row-oriented format.A row-oriented representation of arrow data, that is normalized for comparison
Configure the data type and sort order for a given column