How can add a name of table by concatenating strings?

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Zeynab Mousavikhamene 2020-1-31

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编辑： Stephen23 2020-2-6

I have multiple matlab tables that at first I need load them to the matlab and then do some analysis. Assume they are saved with these names: tableA, tableB, tableC. I am interested to load all in one array by defining the name of tables in one array:

A=['tableA','tableB','tablesC']

so that I can write a for loop to load all arrays instead of writing load for each individual table. Sth like:

for i=1:size(A)
    load(A(i))
end

and it wont work because A(i) are strings not the name of tables.

How can I solve this issue?

It is more genreal question. It happens to me in many cases that I need to make the name of table by strcat function.

How can I do that?

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BN 2020-1-31

编辑：BN 2020-1-31

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I'm not sure why you require to do this because TUTORIAL: Why Variables Should Not Be Named Dynamically (eval) you can probably fix your problem by store all your tables in a cell array.

D = 'D:\whatever'; % select directory
filePattern = fullfile(D, '*.mat'); %or if you have .xlsx tables
file = dir(filePattern);
x = {};
for z = 1 : numel(file)
    baseFileName = file(z).name;
    fullFileName = fullfile(D, baseFileName);
    x{z} = load(fullFileName); %or readtable if you have .xlsx tables
    fprintf('read file %s\n', fullFileName);
end

then you can simply access each table using something like:

mytable = x(:,1)

let me know if it worked for you !

Stephen23 2020-2-1

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"It happens to me in many cases that I need to make the name of table by strcat function."

Forcing numbers or any other meta-data into variable names is a sign that you are doing something wrong:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

"How can I solve this issue?"

Use arrays and indexing. You can trivially load into an output variable (which is a scalar structure):

S = load(...);

and then use indexing to allocate that array to a non-scalar structure or a cell array... and is exactly what the MATLAB documentation recommends:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

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采纳的回答

Walter Roberson 2020-1-31

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Don't do that!

filenames = something appropriate ;
nfiles = length(filenames);
tcell = cell(nfiles, 1);
for k=1:nfiles
  filestruct = load(filenames{k});
  fn = fieldnames(filestruct);
  tcell{k} = filestruct.(fn{1});
end
A = vertcat(tcell{:}) ;

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Walter Roberson 2020-2-6

Hmmm, my code does not add dynamic names to the structure, or at least not deliberately, but I guess it would not be completely wrong to argue that the way I use load() is a use of dynamic field names. MATLAB automatically creates the field names in that case, rather than my deliberately creating them. I read from them rather than writing to them. If the variable names in the file were fixed then even this would not be needed.

Stephen23 2020-2-6

编辑：Stephen23 2020-2-6

"I wanted to make dynamic name for the table which is not recommended."

Correct: accessing variable names dynamically is not recommended by experienced MATLAB users, and is also very clearly discouraged by the MATLAB documentation:

https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

"Walter's code add dynamic name to structure not directly to the table (which is not recommended)."

I don't see that advice anywhere in the MATLAB documentation. While it is certainly possible to misuse dynamically named fields (e.g. where a non-scalar structure with indexing would be simpler and more effiicient) in general I see no reason to avoid them, especially in your case when it is the much better option.

Most of the risks/disadvantages to dynamically naming variables, such as those I list here:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

do not apply to dynamically named fields, perhaps efficiency could be relevant.

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