CODEWITHSUNDEEP
matlab
Star
Star

Reputation: 2299

Preallocating the space in Matlab without knowing the size?

I am constructing a vector X in Matlab by concatenating the outcomes of each iteration in a loop procedure.

What I am doing at the moment is 

X=[];
for j=1:N
    %do something that delivers a vector A
    %X=[X;A]
end

It is not possible to predict a priori the size of A. Is there any way in which I can preallocate the space?

Upvotes: 2

Views: 432

Answers (1)

Sardar Usama
Sardar Usama

Reputation: 19689

A possible solution:

A=cell(1,N); %Pre-allocating A instead of X as a cell array
for k=1:N    %I changed the name of loop variable since `j` is reserved for imag numbers
  %Here I am generating a matrix of 5 columns and random number of rows. 
  %I kept number of columns to be constant (5) because you used X=[X;A] 
  %in the question which means number of columns will always be same
  A{k} =  rand(randi([1,10],1,1),5); %doing something that delivers a vector A   
end
X = vertcat(A{:});

Upvotes: 6

Related Questions