Making Dynamic array

I want to creat an array that is dynamic in size. I mean I dont know what is going to be the size of array. I just want to insert every upcoming number on the head of array. Tell me the syntax of this and show me the code to find max num in this array at the end. Thanks

Answer 1

[Oleg Komarov]

What do you need it for?

There's no such thing as a dynamic array but you can grow an array with concatenation which is usually not recommended (or was not recommended).

If you have:

A = rand(10,1);

You can grow it as:

A = [A; rand(5,1)];

Such practice very often can be avoided.

Read the first 4 chapters of the getting started guide to see more examples of basi array operations.

[Khawaja Asim]

do you know about any buit-in code for finding max num from an array..??

[Oleg Komarov]

In the command vindow type:

doc max

[Oleg Komarov]

If you know k and it's last value then you don't need to grow it and as I said this practice is (was) not recommended:

for k = 1:10

A(k) = k;

end

This copy-writes the entire array at each iteration and it lead to performance degradation. With the release 2011a things changed.

Answer 2

[Hooman Sedghamiz]

As others correctly noted, it is not a good practice to use a not pre-allocated array as it highly reduces your running speed.

Solution 1: In fact it is possible to have dynamic structures in Matlab environment too. However, it is not a native Matlab structure. Recently, I had to write a graph traversal script in Matlab that required a dynamic stack. To do so, you can simply use a Stack from java libraries for example. It is quite powerful and you can handle almost all different types of data! You can simply borrow this from java within matlab by;

% imports stack utility from java in matlab
import java.util.*;
% then use following commands to deal with stack
A = Stack();
A.push(i); % inserts i on top of stack A
A.pop(); %pops out an element

Solution 2: When I deal with arrays that I do not have any idea how big they have to be, I normally initialize them with an overestimated large size, then assign a counter to them and remove the nonused part in the end of the script. For example:

% Let A be the array that i am going to use, Initialize to large number
  A = zeros(1,1000000);
  % assign a counter that tracks the actual size of your array 
  counter = 1;
  % an arbitrary while loop
  rn = 0;
  while rn ~= 8
   A(counter) = rn;
   rn = randi(10,1,1);
   counter = counter + 1;
  end
  A = A(1:counter-1); % removes the rest of non used array

Hope that was what you were looking for! Cheers

[Zeljko Tomicevic]

Hooman Sedghamiz is it the same with two dimensional array? For example:

    % Let A be the array that i am going to use, Initialize to large number
  A = zeros(1,1000000);
  % assign a counter that tracks the actual size of your array 
  counter = 1;
  % an arbitrary while loop
  rn = 0;
  while rn ~= 8
   A(:, counter) = zeroes(1,11);
   rn = rn + 1;
   counter = counter + 1;
  end
  end

That example works in Matlab but not in Simulink User defined function block Matlab fcn. Simulink returns: Subscripted assignment dimension mismatch: [1] ~= [11]

Best

[Guillaume]

"That example works in Matlab" Not with my version of matlab!

Note that since you defined A with one row A(:, counter) is the same as A(counter), it is a scalar. You cannot assign a 1x11 array to a scalar.

As for your question, it would be very unusual to have a 2D dimensional array whose both dimension are unknown ahead of time, so just make the unknown dimension larger and declare the other one the right size to start with:

A = zeros(100000, 11);
counter = 1; 
while rand < .95 && counter <= size(A, 1)
    A(counter, :) = randi(100, 1, 11);
    counter = counter + 1;
end
A(counter:end, :) = [];

Answer 3

[Khawaja Asim]

Array=[] this leads us to a dynamic array... just run a loop and assign it a value in this way Array(k)=___;

[saumya srivastava]

thank you

Answer 4

[Mohit Kumar]

%dynamic matrix 
%no need to ask the dimensions from user 
%just enter values get the matrix
function matrix = dynamic_matrix()
disp("Enter matrix's element row wise--");
disp('Press enter two times to exit from matrix--');
matrix=[];
while true
    str=input('','s');
    if isempty(str)
        break;
    end
    [row,~,errmsg]=sscanf(str,'%f');  % getting row in column vector
    if ~isempty(errmsg)
    error(errmsg);
    end
    matrix=[matrix row];   % column catenation 
end
matrix=matrix';    % transpose for desire result
disp(matrix);
end

[pramod kumar]

actually i am going to use dynamics data for analysis of force but i do not know the size of data how can i tackle it. i write a loop for it but when it is a single value only then it is workin but i take whole size like j=1:1:1401 it is showing errors. please guide me