Create a new array over each iteration

2021 6 14
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更新时间：2021 6 16
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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,:);

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Rik
Rik 2021-6-14
Ran in:
Ran in:
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
Riccardo Tronconi 2021-6-14
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
Rik 2021-6-14
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
Riccardo Tronconi 2021-6-14
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
Rik 2021-6-14
Why do you want numbered variables? They force you to write difficult and buggy code.
Riccardo Tronconi
Riccardo Tronconi 2021-6-14
I need it parametric so Its functioning is still valid if max(indices) is either lower or greater.
Stephen23
Stephen23 2021-6-15
"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.

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Rik
Rik 2021-6-14
Ran in:

1 个投票

Ran in:
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]}

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Riccardo Tronconi
Riccardo Tronconi 2021-6-15
编辑：Riccardo Tronconi 2021-6-15
Another question: How can I manage values inside for instance my_data{1}?
To indexing for example in a for loop
Stephen23
Stephen23 2021-6-15
"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
Riccardo Tronconi 2021-6-16
编辑：Rik 2021-6-16
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
Rik 2021-6-16
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.

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