Create a new array over each iteration

Hi guys! Starting from one table (A) I would divide it in n-table according to the max value of the A(:,4). At this point every each iteration I must create another table as it follows:

function [T_num2str(i)] = par(A)
n= max(A{:,4});
for i=1:n
    search =  find(A{:,4}==i);
    eval(['T_' num2str(i) ' = table;']);
    T_num2str(i)  = position(search,:);
end 
end

I have two problem:

1- How to define output values if I do not know how many they would be?

2- How to solve this indexing problem ?

T_num2str(i)  = position(search,:);

[Rik]

This is an example of the XY problem. Why don't you explain what you want to do? Your use of eval alone already suggests there is probably a better solution.

My guess would be that a solution would involve a comma separated list:

c=cell(1,3);
[c{:}]=ndgrid(1:2,2:3,4);
format compact,celldisp(c)

c{1} =
     1     1
     2     2
c{2} =
     2     3
     2     3
c{3} =
     4     4
     4     4

How exactly you can use this concept for your problem, depends on what you actually want to do.

[Riccardo Tronconi]

According to ex. in the fouth coloumn I have numbers from 1 to 3. For this purpose, I have created an if statement in the fouth coloum and once is true I have to create a new array (mx6) in which I store each rows .

[Rik]

It is not clear to me what you want to have as an output variable. Can you give a hard-coded example?

%for example:
data_I_want=...
    [2.693613716 2.652678399;
    3.577557088 3.49910799;
    2.56422065 2.604867068;
    3.573647731 3.550236118;
    2.661032734 2.607972076;
    3.541105827 3.585182487];

[Riccardo Tronconi]

data_I_want1=

[ Location 1.61E+18 lab 1 2.693614 3.577557

Location 1.61E+18 lab 1 2.652678 3.49910799

Location 1.61E+18 lab 1 2.666976 3.5399065

Location 1.61E+18 lab 1 2.620591 3.50225475 ]

data_I_want2=

[ Location 1.61E+18 lab 2 2.564221 3.57364773

Location 1.61E+18 lab 2 2.604867 3.55023612

Location 1.61E+18 lab 2 2.699815 3.53594614

Location 1.61E+18 lab 2 2.614945 3.58736603 ]

Same for 3

[Rik]

Why do you want numbered variables? They force you to write difficult and buggy code.

[Riccardo Tronconi]

I need it parametric so Its functioning is still valid if max(indices) is either lower or greater.

[Stephen23]

"I need it parametric so Its functioning is still valid if max(indices) is either lower or greater. "

Sure, but you did not answer Rik's question.

So far there is no obvious reason why you cannot use simpler indexing, rather than your complex and inefficient approach.

Answer 1

[Rik]

The code below gives you what you want. The only difference is that you need to write my_data{1} instead of my_data1.

[~,~,data]=xlsread('ex[1].xlsx')

data = 12×6 cell array
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6936]}    {[3.5776]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[2]}    {[2.5642]}    {[3.5736]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[3]}    {[2.6610]}    {[3.5411]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[2]}    {[2.6049]}    {[3.5502]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[3]}    {[2.6080]}    {[3.5852]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[3]}    {[2.6523]}    {[3.5085]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[3]}    {[2.6343]}    {[3.5355]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[2]}    {[2.6998]}    {[3.5359]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[2]}    {[2.6149]}    {[3.5874]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6527]}    {[3.4991]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6670]}    {[3.5399]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6206]}    {[3.5023]}

indices=cell2mat(data(:,4));
my_data=cell(max(indices),1)
for n=1:max(indices)
    my_data{n}=data(indices==n,:);
end
my_data

my_data = 3×1 cell array
    {4×6 cell}
    {4×6 cell}
    {4×6 cell}

my_data{1}

ans = 4×6 cell array
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6936]}    {[3.5776]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6527]}    {[3.4991]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6670]}    {[3.5399]}
    {'Location'}    {[1.6149e+18]}    {'lab'}    {[1]}    {[2.6206]}    {[3.5023]}

[Riccardo Tronconi]

Another question: How can I manage values inside for instance my_data{1}?

To indexing for example in a for loop

[Stephen23]

"How can I manage values inside for instance my_data{1}?"

What do you mean "manage"?

You can access the arrays using indexing, exactly as you show. For example, my_data{1} is the first array. you can do anything with that array, just like you would any other array.

It is not clear therefore what your question is.

[Riccardo Tronconi]

for i=1:length(my_data{1})
if my_data{1}{i,5} >= 2
% do some calculation
end 
end

Doing so It returns me an error

[Rik]

You made the mistake of using length and assuming it would return the number of rows. The length function does not guarantee that. Use size(my_data{1},1) instead if you want the number of rows. You might also want to learn about the numel function if you want to loop over all elements of an array.