MATLAB: Importing multiple txt files using a combination of for loop and eval

data importfor loopMATLAB

Hello.

I have .txt files with some texts (name of variables on the first row) and numbers, so I can't use "load". I would like to extract just numbers in text files (result1.txt, result2.txt … result50.txt) at once.

If I do…

 for i=1:50
  eval(['txtfile' num2str(i) '= importdata(result' num2str(i) '.txt)']);
 end

I get an error message "Undefined variable "result1" or class "result1.txt"". Even if I place ' ' or " " like

 eval(['txtfile' num2str(i) '= importdata('result' num2str(i) '.txt')']);

and

 eval(['txtfile' num2str(i) '= importdata("result' num2str(i) '.txt")']);,

neither of them works. What should I do? Any suggestions are appreciated.

Best Answer

Don't use evil eval for this...see the FAQ (there's also examples in the doc's now)

http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

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MATLAB: Fprintf in nested for loops

"Able to get the file opening to work"

Well, no, not really. What you've done is alias sprintf to a variable by assigning it in what looks to be array indexing syntax--

>> i=1;j=1;  % assign initial values
   fname=['filei' num2str(i) 'j' num2str(j) '.txt'];  % ok
   fidsum=j+(i-1)*4;                                  % fidsum --> 1 ok, but not sure what intend
   sprintf('fid%d',fidsum)=fopen(fname,'w');     % it all goes south here...
>>
>> whos sprintf
Name           Size            Bytes  Class     Attributes
sprintf      105x1               840  double              
>> which sprintf
sprintf is a variable.
>>

Do you really need all these files open at one time would be first question...but if do, keep the handles in an array...

I=3; J=4;           % loop limits
fid=zeros(I,J);     % preallocate to hold way too many fids at once in all likelihood
for i=1:I
  for j=1:J
    fname=sprintf('filei%02dj%02d.txt',i,j);  % build a file name
    fid(i,j)=fopen(fname,'w');                % and open a file, return fid in array  
  end
end

I don't know what part the fidsum variable was to play so left it out...

Now, when you're ready to write to one of these, then you'd have to know which i, j index pair you want and would write something like

fprintf(fid(i,j),fmt,variables)

but it's highly unlikely you really, really need that many files at once.

What is the actual end objective you're wanting to output? Almost certainly there's a far better way to construct the logic to do so.

MATLAB: Displaying a string using a variable inside a loop

 for i=1:a
 in=input(['Wich is the number ' num2str(i) '?:']); 
 eval (['b' num2str(i) '=in' ';']);
 end

Best Answer

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MATLAB: Fprintf in nested for loops

MATLAB: Displaying a string using a variable inside a loop

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