create number of arrays dynamicly

i have a matrix of [m,n], i want to create m arrays and store those m rows into those m arrays. any way of doing that? example: a=[1 2 3 4;5 6 7 8;9 10 11 12] this matrix has 3 rows so i want to create three arrays(A1,A2,A3) and store A1=[1 2 3 4] A2=[5 6 7 8] A3=[9 10 11 12] thanks in advance

Answer 1

[Walter Roberson]

Don't do that.

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

a_by_row = mat2cell(a, ones(1,size(a,1)), size(a,2));

now a_by_row{K} is the K'th row . You do not need one variable per row.

[Himanshu Tomar]

but i want these arrays to be visible in my workspace.

[Guillaume]

@Walter,

a_by_row = num2cell(a, 2);

is simpler

Answer 2

[Guillaume]

"but i want these arrays to be visible in my workspace"

Why would you want that? If they are different variables, you can't loop over them, you can't process them generically, you can't extend your code to have more arrays, etc.

It's simply bad practice, has lots of downside, and no obvious advantage.

Compare:

%split the matrix into row vectors, REGARDLESS OF THE NUMBER OF ROWS
a_by_row = num2cell(a, 2);  
%send the individual arrays to the same function
%REGARDLESS OF THE NUMBER OF ROWS
for row = 1:numel(a_by_rows)
   dosomething(a_by_row{row});
end
%concatenate the arrays, REGARDLESS OF THE NUMBER OF ROWS
catarray = cat(1, a_by_rows{:});
%etc.

With:

%split into individual variables
for row = 1:size(a, 1)
   eval(sprintf('A%1$d = a(%1$d, :)', row)); %how do you debug that ?
end
%call function on each variable, welcome to copy-paste (or more eval?)
dosomething(A1);
dosomething(A2);
dosomething(A3);
%now if you add more rows, you need to copy-paste more
%concatenate the arrays:
cat(1, A1, A2, A3); %again more copy-paste if more rows.

Answer 3

[Stephen23]

Do NOT create arrays dynamically. Creating arrays dynamically is a really bad way to program. Read this to know why:

http://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat

Better Solution

Instead you could put the arrays into a cell array:

>> a=[1 2 3 4;5 6 7 8;9 10 11 12]
a =
    1    2    3    4
    5    6    7    8
    9   10   11   12

>> X = num2cell(a,2);
>> X{:}
ans =
   1   2   3   4
ans =
   5   6   7   8
ans =
    9   10   11   12

Best Solution

However the best solution would be to leave the data exactly as it is in the numeric array. Just loop over the rows of the data matrix. There is no point in splitting this data up into smaller arrays.

[Himanshu Tomar]

but i want these three arrays in my workspace.

[Stephen23]

They are in your workspace, in the cell array X.

What do you want to do with them? How do you want to use them?

If you tell us what you are trying to do we can show you an efficient way of doing it.

[Walter Roberson]

Did you read the links?

[Himanshu Tomar]

im ploting these elements in that array. example: my GUI is searching for cordinates in the workspace A1=[1 2 3 4] so for me my cordinates are (1,2) and (3,4) and i want to plot this two points whatever you have suggested will may only one variable in my workspace and inside this it will have the cordinates. by doing this my GUI is detecting only one variable and i cant plot it

[Stephen23]

Loop over X, and plot it in the loop.