Selection::points throws a runtime error as it only accepts 2D array and then shows runtime error ndim (1) != array ndim (2)

[robinpaul85]

I am trying to query non-contiguous parts of a matrix in a single HDF5 query. For this I am try to use Selection::points. It seems Selection:points needs a 2D array other wise it throws a compilation error. However when I put in a 2D array (points2) it gives a runtime error Error: Selection ndim (1) != array ndim (2)

In general, I feel better documentation and examples should be provided regarding how to use this functions.

use hdf5::Selection;
use hdf5::{File, Result};
use ndarray::array;
use ndarray::Array1;
use ndarray::Array2;

fn main() -> Result<()> {
    // Step 3: Create an HDF5 file and dataset
    let file = File::create("example.h5")?;
    let dataset = file
        .new_dataset::<f64>()
        .shape((10, 10))
        .create("dataset")?;

    // Initialize the dataset with some data
    let data: Array2<f64> = Array2::from_shape_fn((10, 10), |(i, j)| (i * 10 + j + 1) as f64);

    println!("data:{:?}", data);
    dataset.write(&data)?;

    // Step 4: Define point selection to read non-contiguous parts of a matrix

    // Define the points to select (row, column)
    let points2: Array2<usize> = Array2::from_shape_vec((3, 2), vec![0, 2, 3, 5, 7, 9]).unwrap();
    let points: Array1<usize> = array![0, 3, 7, 9];
    println!("points ndim:{:?}", points.ndim());
    println!("points ndim:{:?}", points2.ndim());
    println!("points:{}", points);
    println!("points2:{}", points2);
    // Read the selected points from the dataset
    //let array2: Array2<f64> = dataset.read_slice_2d(Selection::Points(points2))?; // Gives a compilation error asking add 2D array.
    let array2: Array2<f64> = dataset.read_slice_2d(Selection::Points(points2))?;  // This compiles, but gives a runtime error: Error: Selection ndim (1) != array ndim (2) 
    println!("Read non-contiguous matrix points: {:?}", array2);
    Ok(())
}```

[magnusuMET]

I think it is working as expected as points will always be output as a 1D vector, and you are requesting a 2D output (read_slice_2d). You can modify your script as below to read the specified points.

let array: Array1<f64> = dataset.read_slice(Selection::Points(points2))?;

[robinpaul85]

Is it possible to implement Lines within selection ? For querying a row, I will then have to list all the individual cells in that row.

[magnusuMET]

If you want a hyperslab you can use items such as

let subselector = (4, 3..=8, ..);
let all_selector = ..;
let ndarray_selector = ndarray::s![/* items here */];

Or if you want strides and blocks: a Vec of SliceOrIndex