Trait ndarray_npy::ViewNpyExt

source ·

pub trait ViewNpyExt<'a>: Sized {
    // Required method
    fn view_npy(buf: &'a [u8]) -> Result<Self, ViewNpyError>;
}

Expand description

Extension trait for creating an ArrayView from a buffer containing an .npy file.

The primary use-case for this is viewing a memory-mapped .npy file.

§Notes

For types for which not all bit patterns are valid, such as bool, the implementation iterates over all of the elements when creating the view to ensure they have a valid bit pattern.
The data in the buffer must be properly aligned for the element type. Typically, this should not be a concern for memory-mapped files (unless an option like MAP_FIXED is used), since memory mappings are usually aligned to a page boundary, and the .npy format has padding such that the header size is a multiple of 64 bytes.

§Example

This is an example of opening a readonly memory-mapped file as an ArrayView.

This example uses the memmap2 crate because that appears to be the best-maintained memory-mapping crate at the moment, but view_npy takes a &[u8] instead of a file so that you can use the memory-mapping crate you’re most comfortable with.

use memmap2::Mmap;
use ndarray::ArrayView2;
use ndarray_npy::ViewNpyExt;
use std::fs::File;

let file = File::open("resources/array.npy")?;
let mmap = unsafe { Mmap::map(&file)? };
let view = ArrayView2::<i32>::view_npy(&mmap)?;