Does anyone know if multik has something like np.r...

# mathematics

[Big Chungus]

Does anyone know if multik has something like np.roll() for d2Array?

[Pavel Gorgulov]

Unfortunately, there is no such method in multik

[Big Chungus]

Are you aware of any alternatives for kotlin?

[Big Chungus]

Or any articles that would allow me to implement one myself?

[Pavel Gorgulov]

For any dimension?

[Big Chungus]

I'm working with d2Array

[Pavel Gorgulov]

roll without specifying an axis, it’s just a shift.
You can use `Collections.rotate`:

fun D2Array<Int>.roll(n: Int): D2Array<Int> {
    val data = this.toList().also { Collections.rotate(it, n) }
    return D2Array(MemoryViewIntArray(data.toIntArray()), shape = this.shape.clone(), dim = this.dim)
}

or use sliceArray

fun D2Array<Int>.roll(n: Int): D2Array<Int> {
    val newData = this.data.getIntArray().let { it.sliceArray(size - n until size) + it.sliceArray(0 until size - n) }
    return D2Array(MemoryViewIntArray(newData), shape = this.shape.clone(), dim = this.dim)
}

[Big Chungus]

I do need an axis though 😄 Here's what I'm trying to do

img = np.roll(img, dy, axis=0)
 img = np.roll(img, dx, axis=1)

[Big Chungus]

img is a 2d array

[Pavel Gorgulov]

with axes are more complicated
There are no functions from kotlin for this, here need to work with strides

[Big Chungus]

Might sound a bit dense, but what do axes mean in 2darray context here?

[Pavel Gorgulov]

Same as in numpy, axis(1) by columns or axis(0) by rows

[Big Chungus]

🤦‍♂️ so basically dimensions. Thought so...

[altavir]

In KMathe it is planed to do that with virtual buffers. But manipulating strides is a more performant solution. I wonder if roll have a lot of uses outside numpy paradigm (I meant when you can't work with elements in a cycle). @Big Chungus could you explain the problem you are solving.

[Big Chungus]

Not sure I can. I'm basically getting my feet wet with OpenCV and image transformations. Here's a PY algorithm I'm trying to reproduce to shift image https://stackoverflow.com/a/53140617

[Big Chungus]

Also kmath seems massive, but the missing docs makes it extremey hard to get started (I've been trying for the entire day today 😄 )

[altavir]

Yeah, a lot of holes in it and too many experiments so far. For simple 2d manipulation Multik could be better so far.