# Crate ndarray_slice

Expand description

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.

ResourceComplexitySorting (stable)Sorting (unstable)Selection (unstable)Bulk Selection (unstable)
TimeBestO(n)O(n)O(n)O(n log m)
TimeAverageO(n log n)O(n log n)O(n)O(n log m)
TimeWorstO(n log n)O(n log n)O(n)O(n log m)
SpaceBestO(1)O(1)O(1)O(m)
SpaceAverageO(n/2)O(log n)O(1)O(m+log m)
SpaceWorstO(n/2)O(log n)O(1)O(m+log m)

• 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`.
• `stacker` for spilling recursion stack over to heap if necessary. Enabled by `default`.
• `rayon` for parallel `par_sort*`/`par_select_many_nth_unstable*`.

## Re-exports§

• `pub use ndarray;`