for loop with eval and sprintf with underscore in

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Elisa 2014-4-7

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编辑： Stephen23 2023-11-14

Sorry about that,

I've been trying really hard to find any solution from other answers, but or I don't understand them or it doesn't work.

I've also red that is bad to dynamically use 'eval' and 'sprintf', however, even though I'm willing to learn, I am not able to do in another way (and I've tried it).

I've many .txt file:

X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt

% Load .txt files into workspace
    files = dir('*.txt');
for i=1:length(files); 
        eval(['load ' files(i).name ' -ascii']);
end
%% I dynamically try to do something with my variable
for i=1:length(files);  
      filename = files(i).name(1:end-4); %%%I get out the .txt
        temp = eval(sprintf('X%s\_1\_ABC\_ABCD\_ABCDE\_ABCDEF',filename));
 %insert the matrix of the text file into a new 3D matrix 
          threeD_matrix (i,:,f) = temp;      
  end

Warning: Escape sequence '_' is not valid. See 'help sprintf' for valid escape sequences. Error using eval Undefined function or variable

Thank you so much for your help!!!!!

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Stephen23 2023-11-14

编辑：Stephen23 2023-11-14

"I've many .txt file: X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt"

The simple solution is to avoid LOAD for textfiles. Use READMATRIX, READTABLE, etc.

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

At the time this question was posted, CSVREAD or DLMREAD would likely have worked.

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回答（2 个）

Jan 2014-4-7

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在 MATLAB Online 中打开

Two general advices:

1. Avoid eval in general:

eval(['load ' files(i).name ' -ascii']);

Better:

load(files(i).name, '-ascii');

2. Join folder names by fullfile instead of sprintf with hard coded separators.

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Elisa 2014-4-8

Thanks Jan! I didn't know, who to do it! I'll follow your tips for next time! Thanks a lot!

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Star Strider 2014-4-7

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编辑：Star Strider 2014-4-7

在 MATLAB Online 中打开

To put a backslash (\) into a string, you need to use a double backslash (\\):

filename = 'myfile.txt';
R = sprintf('X%s\\_1\\_ABC\\_ABCD\\_ABCDE\\_ABCDEF', filename)

produces:

R =
Xmyfile.txt\_1\_ABC\_ABCD\_ABCDE\_ABCDEF

The ‘eval’ function is not considered efficient programming practice, but it may be the only way to get a variable generated as a string into the workspace as a variable. It is not really ‘wrong’ though.