Crate ndarray_slice

Fast and robust slice-based algorithms (e.g., sorting, selection, search) for non-contiguous (sub)views into n-dimensional arrays. Reimplements algorithms in slice and rayon::slice for ndarray with arbitrary memory layout (e.g., non-contiguous).

Example

use ndarray_slice::{ndarray::arr2, Slice1Ext};

// 2-dimensional array of 4 rows and 5 columns.
let mut v = arr2(&[[-5, 4, 1, -3,  2],   // row 0, axis 0
                   [ 8, 3, 2,  4,  8],   // row 1, axis 0
                   [38, 9, 3,  0,  3],   // row 2, axis 0
                   [ 4, 9, 0,  8, -1]]); // row 3, axis 0
//                    \     \       \
//                  column 0 \    column 4         axis 1
//                         column 2                axis 1

// Mutable subview into the last column.
let mut column = v.column_mut(4);

// Due to row-major memory layout, columns are non-contiguous
// and hence cannot be sorted by viewing them as mutable slices.
assert_eq!(column.as_slice_mut(), None);

// Instead, sorting is specifically implemented for non-contiguous
// mutable (sub)views.
column.sort_unstable();

assert!(v == arr2(&[[-5, 4, 1, -3, -1],
                    [ 8, 3, 2,  4,  2],
                    [38, 9, 3,  0,  3],
                    [ 4, 9, 0,  8,  8]]));
//                                   \
//                                 column 4 sorted, others untouched

Current Implementation

Complexities where n is the length of the (sub)view and m the count of indices to select.

Resource	Complexity	Sorting (stable)	Sorting (unstable)	Selection (unstable)	Bulk Selection (unstable)
Time	Best	O(n)	O(n)	O(n)	O(n log m)
Time	Average	O(n log n)	O(n log n)	O(n)	O(n log m)
Time	Worst	O(n log n)	O(n log n)	O(n)	O(n log m)
Space	Best	O(1)	O(1)	O(1)	O(m)
Space	Average	O(n/2)	O(log n)	O(1)	O(m+log m)
Space	Worst	O(n/2)	O(log n)	O(1)	O(m+log m)

Roadmap

• Add SliceExt trait for n-dimensional array or (sub)view with methods expecting Axis as their first argument. Comparing methods will always be suffixed with _by or _by_key defining how to compare multi-dimensional elements (e.g., rows) along the provided axis of interest (e.g., columns).

Features

• alloc for stable sort/sort_by/sort_by_key. Enabled by std.
• std for stable sort_by_cached_key. Enabled by default or rayon.
• rayon for parallel par_sort*/par_select_many_nth_unstable*.

Re-exports

• pub use ndarray;

Traits

• Slice1Ext
  Extension trait for 1-dimensional ArrayBase<S, Ix1> array or (sub)view with arbitrary memory layout (e.g., non-contiguous) providing methods (e.g., sorting, selection, search) similar to slice and rayon::slice.