set_col() fails

[polarathene]

set_col() docs could do with an example.

It is not clear what the expected array for new_col should look like. I have tried dims [3, 1, 1, 1] and [1, 3, 1 ,1], both times an error was thrown about incorrect size.

let range_a: Vec<u8> = (1..4).collect();
let range_b: Vec<u8> = (4..7).collect();

let dims = Dim4::new(&[1, 3, 1, 1]);
let mut range_a_af = af::Array::new(&range_a, dims);
let     range_b_af = af::Array::new(&range_b, dims);

af_print!("range_a_af:", range_a_af);
// [1 3 1 1]
//          1          2          3 
af_print!("range_b_af:", range_b_af);
// [1 3 1 1]
//          4          5          6

// I'd like all values in a column to be changed to those the values in the given array or the given arrays matching column, I assume for a scalar value I'd use a constant array(sized to elements in the column or matching dims depending how this method works
range_a_af = set_col(&range_a_af, &range_b_af, 0); // should replace 1 with 4?
af_print!("range_a_af == [4, 2, 3]?: ", range_a_af);

This throws the following error:

In function void assign(opencl::Array<T>&, const unsigned int&, const af_seq*, const opencl::Array<outType>&) [with Tout = unsigned char; Tin = unsigned char; af_seq = af_seq]
In file src/api/c/assign.cpp:59
Size mismatch between input and output

thread 'main' panicked at 'Error message: Size is incorrect', /home/pola/.cargo/registry/src/github.com-1ecc6299db9ec823/arrayfire-3.4.3/src/error.rs:66

This might be due to the indexing bug that @9prady9 fixed here. Either that or I've misunderstood how to use this method.

[9prady9]

@polarathene I believe you misunderstood what column means here. Given that your input is [1 3 1 1], there are three columns in the Array and each column has single element. Therefore, the new_col parameter of set_col should be an Array of size 1. Hence, you are seeing an error - your new_col Array is of again [1 3 1 1] size where as the function is expecting [1 1 1 1].

I agree that an example in the functions documentation would definitely and we have an open issue for the same.

[polarathene]

If there were 5 rows of 3 columns([5, 3, 1, 1]), then the new_col dims would be [5,1,1,1]?

[9prady9]

Yes, that is correct.

Array with dimensions [ M N O P ]
has

• N columns
• M rows
• O slices of size MxN

M is number of element in a column
N is number of elements in a row
O is number of elements in a slice of MxN elements

Thus the naming convention of set_[row | col | slice] and get_[row | col | slice] functions.

[polarathene]

I was familiar with row and col, I noticed slice but it didn't click to me that it was related to these two like that for some reason :) I guess the new docs will mention the 3 together like you just did.

I put together an example for using set_col() and col()(Rust wrapper doesn't call it get_col()).

// Showcases usage of `set_col()` and `col()`
fn col_example() {
    let range_a: Vec<u8> = (1..16).collect();
    let range_b: Vec<u8> = (20..26).collect();
    let range_c: Vec<u8> = (30..41).collect();

    // The arrays columns must have the same size(number of rows)
    let dims_a = Dim4::new(&[5, 3, 1, 1]);
    let dims_b = Dim4::new(&[5, 1, 1, 1]);
    let dims_c = Dim4::new(&[5, 2, 1, 1]);

    let mut range_a_af = af::Array::new(&range_a, dims_a);
    let     range_b_af = af::Array::new(&range_b, dims_b);
    let     range_c_af = af::Array::new(&range_c, dims_c);



    af_print!("range_a_af:", range_a_af);
    // [5 3 1 1]
    //      1          6         11
    //      2          7         12
    //      3          8         13
    //      4          9         14
    //      5         10         15
    af_print!("range_b_af:", range_b_af);
    // [5 1 1 1]
    //     20 
    //     21 
    //     22 
    //     23 
    //     24 
    af_print!("range_c_af:", range_c_af);
    // [5 2 1 1]
    //     30         35 
    //     31         36 
    //     32         37 
    //     33         38 
    //     34         39 



    // `range_b_af` only contains 1 column of 5 rows. To replace the first
    // column in `range_a_af`(0):
    range_a_af = set_col(&range_a_af, &range_b_af, 0);

    af_print!("1st column replaced: ", range_a_af);
    // [5 3 1 1]
    //     20          6         11 
    //     21          7         12 
    //     22          8         13 
    //     23          9         14 
    //     24         10         15 



    // Take the 2nd column from `range_c_af`(1) and replace the 3rd column
    // in `range_a_af`(2):
    range_a_af = set_col(&range_a_af, &col(&range_c_af, 1), 2);

    af_print!("3rd column replaced: ", range_a_af);
    // [5 3 1 1]
    //     20          6         35 
    //     21          7         36 
    //     22          8         37 
    //     23          9         38 
    //     24         10         39 
}

[polarathene]

Rust docs for set_col() I think just need brief code snippet and perhaps mention:

The arrays columns must have the same size(number of rows)

[9prady9]

@polarathene My bad, I guessed it is get_*. Can you please send in a PR with the code example added to the function documentation ?

[polarathene]

code example added to the function ?

I've not contributed rust docs before. Is the docs contained within the source? Or did you want the larger snippet in the examples? Happy to send a PR.

[9prady9]

Documentation would be part of source code. You can look at the example written for shift to get an idea of how to write an example.

Also, once you write a test - the command cargo test will run the code stub you add to the documentation - this way you can check that the code snippet you add compiles fine. You can always ping me on gitter if you get stuck anywhere.