MATLAB: How to solve pre-allocating array

endforMATLABpreallocating array

Hello everyone,
I have a coding like this, where I need to extract the row which has same index number in column 5 of my data. Attached is my data,
%Example matrix

A = load('Ntxp0014.txt');
%Find indices to elements in first column of A that satisfy the equality

ind11 = A(:,5) == 11 ;
ind12 = A(:,5) == 12 ;
ind13 = A(:,5) == 13 ;
ind14 = A(:,5) == 14 ;
ind15 = A(:,5) == 15 ;
ind16 = A(:,5) == 16 ;
ind17 = A(:,5) == 17 ;
ind18 = A(:,5) == 18 ;
ind19 = A(:,5) == 19 ;
ind20 = A(:,5) == 20 ;
ind21 = A(:,5) == 21 ;
ind22 = A(:,5) == 22 ;
%Use the logical indices to index into A to return required sub-matrices

A11=A(ind11,:);
A12=A(ind12,:);
A13=A(ind13,:);
A14=A(ind14,:);
A15=A(ind15,:);
A16=A(ind16,:);
A17=A(ind17,:);
A18=A(ind18,:);
A19=A(ind19,:);
A20=A(ind20,:);
A21=A(ind21,:);
A22=A(ind22,:);
but it is not practical when deals with many data. How I would to solve this pre-allocating array? However, I've try using for … end function but still have error. 
%Example matrix
A = load('Ntxp0014.asc');
%Find indices to elements in first column of A that satisfy the equality
for i = 11:364
ind(i) = A(:,5) == i ;
%Use the logical indices to index into A to return required sub-matrices
A(i) = A(ind(i),:);
end

Best Answer

Using numbered variables is a sign that you are doing something wrong.
Accessing numbered variables is one way that beginners force themselves into writing slow, complex, buggy code that is hard to debug. Read this to know why:
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
You can easily avoid that bad code approach by splitting that data into a cell array, either using a simple loop or some other grouping function, for example using arrayfun:
>> A = dlmread('Ntxp0014.txt'); % better than LOAD
>> V = 11:22;
>> F = @(n) A(A(:,5)==n,:);
>> C = arrayfun(F,V,'UniformOutput',false);
Lets check the contents of the first cell (fifth column==V(1)==11):
>> C{1}
ans =
  1.9921e+013  1.84720  95.016  -36.904  11  14
  1.9921e+013  1.79460  95.034  -36.599  11  14
  1.9921e+013  1.74200  95.053  -36.346  11  14
  1.9921e+013  1.68940  95.072  -36.130  11  14
  1.9921e+013  1.63680  95.091  -35.879  11  14
... lots of lines
  1.9921e+013  0.216460  95.597  -28.778  11  14
  1.9921e+013  0.163860  95.616  -28.799  11  14
  1.9921e+013  0.111250  95.635  -28.807  11  14
  1.9921e+013  0.058644  95.653  -28.891  11  14
  1.9921e+013  0.006037  95.672  -28.904  11  14
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