Making Dynamic array

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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

Accepted Answer

Oleg Komarov
Oleg Komarov on 13 Aug 2011
Edited: John Kelly on 26 Feb 2015
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.
Oleg Komarov
Oleg Komarov on 13 Aug 2011
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;
This copy-writes the entire array at each iteration and it lead to performance degradation. With the release 2011a things changed.

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More Answers (4)

Hooman Sedghamiz
Hooman Sedghamiz on 10 Feb 2017
Edited: Hooman Sedghamiz on 10 Feb 2017
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;
A = A(1:counter-1); % removes the rest of non used array
Hope that was what you were looking for! Cheers
Guillaume on 3 Jan 2018
"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;
A(counter:end, :) = [];

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Khawaja Asim
Khawaja Asim on 13 Aug 2011
Array=[] this leads us to a dynamic array... just run a loop and assign it a value in this way Array(k)=___;

Mohit Kumar
Mohit Kumar on 21 Aug 2019
%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--');
while true
if isempty(str)
[row,~,errmsg]=sscanf(str,'%f'); % getting row in column vector
if ~isempty(errmsg)
matrix=[matrix row]; % column catenation
matrix=matrix'; % transpose for desire result
  1 Comment
Chaudhary P Patel
Chaudhary P Patel on 2 Feb 2020
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

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William Bless Steven LAWSON
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var i = 0;
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var newRow = document.createElement('tr');
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  1 Comment
William Bless Steven LAWSON
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