How to index first element of an arbitary sized matrix?

I have a matrix and I need to index the first dimension but I don't know the size of the matrix. Is there a way to do this in a generic way rather than hard code each case. I am aware I could do this with eval but I try and steer clear of using this function where possible.

Example:

ind_left = 25;
ind_right = 66;

% For a 2-D matrix it would be this 
A = rand(100,100); % sample 3-D input matrix
B = A(ind_left:ind_right,:);

% For a 3-D matrix it would  
A = rand(100,100,100); % sample 3-D input matrix
B = A(ind_left:ind_right,:,:);

% For a 4-D matrix it would be ...

[Stephen23]

Note that you can use a comma-separated list for indexing:

A = rand(5,4,3,2);            % arbitrary array
C = repmat({':'},1,ndims(A)); % indices
C{1} = 3:5;                   % indices
B = A(C{:}); % indexing using comma-separated list

For comparison:

C = A(3:5,:,:,:);
isequal(B,C)

ans = logical
   1

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

[Joseph Hansen-Shearer]

This is an even neater solution. Although shouldn't it be

C = repmat({':'},ndims(A),1);

[Stephen23]

@Joseph Hansen-Shearer: thank you for noticing that, I fixed my comment!

Answer 1

[Dyuman Joshi]

%Example
ind_left = 25;
ind_right = 45;
vec = ind_left:ind_right;

n = 5;
A = rand(50*ones(1,n)); % sample n-D input matrix
size(A)

ans = 1×5

50 50 50 50 50

%Manually
B = A(vec,:,:,:,:);
size(B)

ans = 1×5

21 50 50 50 50

%Generalised method
C = reshape(A(vec,:),[numel(vec) size(A, 2:ndims(A))]);
size(C)

%Check for equality
isequal(B,C)

ans = logical
   1

[Joseph Hansen-Shearer]

Amazing thank you so much that is perfect

[Dyuman Joshi]

You are welcome!

[Joseph Hansen-Shearer]

For other people looking the answer by @Stephen23 is neater