Crate transpose

source ·
Expand description

Utility for transposing multi-dimensional data stored as a flat slice

This library treats Rust slices as flattened row-major 2D arrays, and provides functions to transpose these 2D arrays, so that the row data becomes the column data, and vice versa.

// Create a 2D array in row-major order: the rows of our 2D array are contiguous,
// and the columns are strided
let input_array = vec![ 1, 2, 3,
						4, 5, 6];
 
// Treat our 6-element array as a 2D 3x2 array, and transpose it to a 2x3 array
let mut output_array = vec![0; 6];
transpose::transpose(&input_array, &mut output_array, 3, 2);

// The rows have become the columns, and the columns have become the rows
let expected_array =  vec![ 1, 4,
							2, 5,
							3, 6];
assert_eq!(output_array, expected_array);

// If we transpose our data again, we should get our original data back.
let mut final_array = vec![0; 6];
transpose::transpose(&output_array, &mut final_array, 2, 3);
assert_eq!(final_array, input_array);

This library supports both in-place and out-of-place transposes. The out-of-place transpose is much, much faster than the in-place transpose – the in-place transpose should only be used in situations where the system doesn’t have enough memory to do an out-of-place transpose.

The out-of-place transpose uses one out of three different algorithms depending on the length of the input array.

  • Small: simple iteration over the array.
  • Medium: divide the array into tiles of fixed size, and process each tile separately.
  • Large: recursively split the array into smaller parts until each part is of a good size for the tiling algorithm, and then transpose each part.

Functions§