How do I loop trough variables

Question

René Moerman 2020-3-6

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评论： Guillaume 2020-3-6

How do I loop throug variables like this?
a=1;
b=2;
c=3;
for Q=[a b c]
    Y=Q
end

The result i would like is:

y = 1
y = 2 
y = 3

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Guillaume 2020-3-6

编辑：Guillaume 2020-3-6

Are the variables actually tables which would show in the variable browser as a 9x14 table, or cell arrays which would show in the variable browser as 9x14 cell?

Also, what do you want to do with your loop?

René Moerman 2020-3-6

在 MATLAB Online 中打开

They are cell arrays,

S1R1, S1R2, S1R3 ...... are my measurement positions from my experiment. They are cell arrays with in every collumn a different parameter.

I want to loop these variables so I can go through all my measurement positions and then extract the parameters i want from these positions so I can plot them.

like this:

for Q = [S1R1 S1R2 S1R3 ect. ect.]
    
    F = Q(2:end,1);
    F = cell2mat(F);
    T30 = Q(2:end,2);
    T30 = cell2mat(T30);
    rT30 = Q(2:end,3);
    rT30 = cell2mat(rT30);
    T20 = Q(2:end,4);
    T20 = cell2mat(T20);
    semilogx(F,T30)
    hold on
end

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Answer 1

Stephen23 2020-3-6

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编辑：Stephen23 2020-3-6

在 MATLAB Online 中打开

"Why is that?"

Your confusion stems from several things.

[] square brackets are a concatenation operator, not a "list" operator (which MATLAB does not have). So you took three 9x14 cell arrays and concatenated them horizontally to get one 9x42 cell array (not a "list" of separate arrays as you seemed to be expecting). If you want to store several arrays in a container, then use a cell array.
Without realizing it, you are looping over the columns of that 9x42 cell array. The for documentation explains that if the values to be iterated over are a non-vector array, then for will iterate over its columns. I have never seen anyone rely on this "feature".

I would avoid your approach of iterating over data or over arrays: it is much more robust to iterate over indices:

C = {arr1,arr2,arr3}; % cell array
for k = 1:numel(C)
    Y = C{k};
    ... do whatever with Y
end

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Guillaume 2020-3-6

"I have never seen anyone rely on this "feature"."

I use it sometimes, but it is indeed very rare that you just want to iterate over columns without knowing their indices.

Guillaume 2020-3-6

"would avoid your approach of iterating over data or over arrays"

Totally agree.

Even better would be to avoid creating these numbered arrays in the first place. There should only be one variable to start with, either a cell array or in this case since all the arrays are the same size, a 3D matrix.

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