Split an array using specific points

Just starting out in matlab and would appreciate your help.

for example : lets say I have an array Y = [5;2;3;6;7;9;5;5;6;3;8;7;74;9;63;47;10;3]; and another array of index diiv = [5;9;15];

How can i use diiv to break Y into smaller arrays so I would get as output arrays y1 = [5;2;3;6;7], y2 =[9;5;5;6]; y3 =[3;8;7;74;9;63]; y4=[47;10;3]

Thanks

[Stephen23]

If you are numbering your variables like that then you are doing something wrong.

If you are trying to access variable names dynamically then you are doing something wrong.

Simple and efficient MATLAB code uses arrays and indexing. You should use arrays and indexing.

Answer 1

[Stephen23]

Simpler and more efficient than what you are attempting (although most likely you don't realise that yet):

Y = [5;2;3;6;7;9;5;5;6;3;8;7;74;9;63;47;10;3];
diiv = [5;9;15];
D = diff([0;diiv;numel(Y)]); % complete the missing data
C = mat2cell(Y,D,1) % split into a cell array

C = 4×1 cell array
    {5×1 double}
    {4×1 double}
    {6×1 double}
    {3×1 double}

C{:}

ans = 5×1

5 2 3 6 7

ans = 4×1

9 5 5 6

ans = 6×1

3 8 7 74 9 63

ans = 3×1

47 10 3

See also: https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html

[Daniel Adeniyi]

Oh this is just perfect. I understand what you mean by using indexing. this is a better solution.

[Stephen23]

@Daniel Adeniyi: if my answer helped you please click the accept button.

Answer 2

[Alan Stevens]

Like this?

Y = [5;2;3;6;7;9;5;5;6;3;8;7;74;9;63;47;10;3];
diiv = [5; 9; 15];
y1 = Y(1:diiv(1));
y2 = Y(diiv(1)+1:diiv(2));
y3 = Y(diiv(2)+1:diiv(3));
y4 = Y(diiv(3)+1:end);

[Daniel Adeniyi]

Yes something like this, but is it possible to do this automatically (like in a loop) without writing out each expression for y1, y2,y3,y4

[Stephen23]

"is it possible to do this automatically (like in a loop) without writing out each expression for y1, y2,y3,y4"

It is certainly possible, but only if you want to force yourself into writing slow, complex, inefficient code which is buggy and hard to debug:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

In contrast the neat, simple, and very efficient MATLAB approach is to use indexing.

Tip: if you are numbering your varaible names like that, then you are doing something wrong.

Answer 3

[Matt J]

More likely you would want to do something like this,

y=mat2cell(Y,diiv)

[Daniel Adeniyi]

this gives a dimension error unfortunately as the sum of the elements in diiv is greater than the number of elements in Y.