for loop with eval and sprintf with underscore in

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!!!!!

[Stephen23]

"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.

Answer 1

[Jan]

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.

[Elisa]

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

Answer 2

[Star Strider]

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.

[Elisa]

Dear Star,

Many thanks for your answer.

I need to get the underscore not the backslash, though:

X12345678_1_ABC_ABCD_ABCDE_ABCDEF

Sorry about the confusion!

[Star Strider]

To do that, just put them in as ordinary characters:

filename = 'myfile.txt';
R = sprintf('X%s_1_ABC_ABCD_ABCDE_ABCDEF', filename)

produces:

R =

Xmyfile.txt_1_ABC_ABCD_ABCDE_ABCDEF

[Elisa]

It gives me an error. That is why I am getting crazy with that.

The error says:

Error using eval Undefined function or variable 'X12345678'.

Error in my_script (line 36) temp = eval(sprintf('X%s_1_ABC_ABCD_ABCDE_ABCDEF',filename)); >> Line 36 is the line where we wrote:

   temp = eval(sprintf('X%s_1_ABC_ABCD_ABCDE_ABCDEF',filename));

Thanks for your help!!!!!

[Star Strider]

I believe I’m beginning to understand what you’re doing. To find out what the variables are in your ‘.mat’ files, see the documentation for that version of whos and its friends. (NOTE that there is also a version of whos that operates in a different context but provides the same sort of information. This is the first time I realised there are actually two versions of that function, so thanks!)

I’m not certain what you want to do after you load your files. If this isn’t the direction you want to go with them or the variables in them (since I have no idea how they’re organised and what they contain), please describe in some detail what you want to do.

[Elisa]

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

I have 3 folders. Each of them contains many subfolders, which contains many .txt files. I have written a loop, so, I could open the folder, load the .txt files for each folder and operates with them; then cd back to the folder, open the next one, load the .txt file and operates with them; cd back etc. without having to write their name all the time. therefore I used 'eval' and 'sprintf'.

It 's work for one folder, where the .txt files didn't have such a long name. Now, with this one it doesn't work :(

Error using eval 
Undefined function or variable 'X12345678'.

Error in my_script (line 36) temp = eval(sprintf('X%s_1_ABC_ABCD_ABCDE_ABCDEF',filename));

in fact, the variable is not called 'X12345678' but 'X12345678_1_ABC_ABCD_ABCDE_ABCDEF'

I don't know!!!!

[Star Strider]

My pleasure!

I’m nevertheless still a bit lost.

What happens if you just write:

disp(X12345678_1_ABC_ABCD_ABCDE_ABCDEF)

Does it display the contents of the variable? If so, the variable is already in your workspace.

Since I get the impression that this may actually be a file name, see what this does:

which X12345678_1_ABC_ABCD_ABCDE_ABCDEF -all

If it’s a file in MATLAB’s path, that should find it. You may have to change that to:

which X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt -all

or whatever its extension is. The function version of that command will return the entire file path:

datfile = which('X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt')

or

datfile = which('X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt','-all')

See the documentation for which for more details.

[Elisa]

Dear Star Stride,

Thanks a lot again!

I used

disp(....) and the variable is there

which  X12345678_1_ABC_ABCD_ABCDE_ABCDEF -all

says that:

X12345678_1_ABC_ABCD_ABCDE_ABCDEF is a variable

which X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt -all

says that:

 X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt not found

datfile = which('X12345678_1_ABC_ABCD_ABCDE_ABCDEF.txt','-all')

gives: datfile = {}

[Elisa]

thanks for your help!!!! I'll manually change the annoying name. X12345678 without _1_ABC_ABCD_ABCDE_ABCDEF.txt works fine strangely.

[Star Strider]

My pleasure!

Sorry for the delay — sleeping here (GMT-6).

[Star Strider]

My pleasure!

Sorry for the delay — sleeping here (GMT-6).