How to pick elements of several arrays via assigned vector

Hi,

I have 3 arrays, and would like to form new array picking elements from these 3 arrays.

The picking is via my assigned vector.

The computation should be matrix computation, no for loop inside.

e.g.

-----

[input]

arr_i1 = [111,112,113,114; ...

121,122,123,124];

arr_i2 = [211,212,213,214; ...

221,222,223,224];

arr_i3 = [311,312,313,314; ...

321,322,323,324];

vec_i = [2,3,1,2];

[output]

arr_o = [211,312,113,214; ...

221,322,123,224];

-----

Your answer would be quite appreciated.

[KSSV]

How you got the output? Check the indices properly.

Also it is not advisable to have arr_i1,arr_i2 etc.

[SALAH ALRABEEI]

what is exactly do you want! How the vec_i is related to the matrix index!

[Warren Chuo]

@KSSV

@SALAH ALRABEEI

Thank you for comments.

To make my question more clear:

arr_i = cat(3,arr_i1,arr_i2,arr_i3);

the function(e.g. func_pick) I want to seek is

arr_o = func_pick(arr_i,vec_i);

Detail in/out relationship of this function is:

arr_o(1:2,1) = arr_i(1:2,1,2), since vec_i(1) == 2;

arr_o(1:2,2) = arr_i(1:2,2,3), since vec_i(2) == 3;

arr_o(1:2,3) = arr_i(1:2,3,1), since vec_i(3) == 1;

arr_o(1:2,4) = arr_i(1:2,4,2), since vec_i(4) == 2;

Answer 1

[Shivam Malviya]

Hi Warren!

You can find the implementation of the func_pick function below: -

func_pick.m

function arr_o = func_pick(arr_i, v)
    d3 = v;
    d2 = 1:length(d3);
    d1 = [1:size(arr_i, 1)]';

    i1 = repmat(d1, 1, length(d2));
    i2 = repmat(d2, length(d1), 1);
    i3 = repmat(d3, length(d1), 1);
    i123 = cat(3, i1, i2, i3) - 1;

    linear_i = i123(:, :, 1) + size(arr_i, 1) * (i123(:, :, 2) + size(arr_i, 2) * i123(:, :, 3)) + 1
    arr_o = arr_i(linear_i);
end

script.m

a1 = [111,112,113,114; 
          121,122,123,124];
a2 = [211,212,213,214; 
          221,222,223,224];
a3 = [311,312,313,314; 
          321,322,323,324];

arr_i = cat(3, a1, a2, a3);
v = [2, 1, 3, 2];
arr_o = func_pick(arr_i ,v)

[Warren Chuo]

Hi, Shivam Malviya,

Thank you for your wise input, and I'm very sorry to respond this late.

Somebody suggested me 'sub2ind' and manipulate indices instead of values.

After few optimizing steps, I found out a straightforward way to just cover my real issues efficiently.

Your suggested function can lead to expected result very well.

Just I need few moment to digest the arithmetic relationship inside this function.

Anyway, your input is very appreciated.