Can one have a function that opens and manipulates more than one file with name containing an array

If in a script named Overall I have :

 angle = input('Which angles (degree) are you targeting: ')
 >> [8 7 6 5 4 3 2 1]

followed by calling function:

 Tablefliptrial(angle) %line 5

and then a create a separate .m file containing the function

 function [desiredOutput] = tablefliptrial(angle)
     fileID = fopen('distance',angle,'zenith.plt'); %open file %line 2
     %do a bunch of operations towards desired output
     desiredOutput = [] %huge matrix
end

Am I allowed to place the value of each angle so that the function reads each file format (i.e. distance1zenith, distance2zenith...) or do I need a different approach? Error given:

 Error using fopen
 Invalid permission.
 Error in Tablefliptrial (line 2)
 fileID = fopen('distance',angle,'zenith.plt'); %open file
 Error in Overall (line 5)
 Tablefliptrial(angle)

Answer 1

[Ameer Hamza]

fopen() can only accept two inputs. The first input is filename and second is the permission. What you are doing, is to give 3 inputs to fopen(). Therefore fopen() is not working. Also each call to fopen() can only open 1 file so you will need to for loop. You need to do it like this

function [desiredOutput] = tablefliptrial(angle)
   for i=angles
     fileID = fopen(['distance',num2str(i),'zenith.plt']); %open file %line 2
     %do a bunch of operations towards desired output
     desiredOutput = [] %huge matrix
   end
end

note that adding [] have converted the three inputs into one char array of the filename. You can specify the second input to fopen() as permission with which you want to open the file.

[fernando aguirre]

Awesome thank you! So how would I save each iteration of desiredOutput based on the index of the angle? I keep getting

 Index exceeds matrix dimensions for line 6:
function [desiredOutPut] = tablefliptrial(angle)
    for i = angle
        fileID = fopen(['distance',num2str(i),'zenith.plt'],'r'); %open file
        A = fscanf(fileID,'%f',[2 Inf]); %read file
        A=A'; %transpose since not in nx2 
        [uniqVals] = unique(A(:,1)) %find unique values of column one %line 6
        ...
        desiredOutput = []
    end
end

After the 3rd loop (shown by displaying i as the loop runs).

Also note that the 6th line is a column of 12,000 values (1x12000)

[Ameer Hamza]

If you are getting an error on this line

[uniqVals] = unique(A(:,1))

then it is probably happening because A is an empty vector. Can you use MATLAB debugger to identify the actual value of A at that line.

Also, you can first run

dbstop if error

this will halt the execution whenever error happen and you can check the value of variables at that line to see what might be causing the issue.

Also if you want to save the value of desired output in each iteration, you can do it as follow

function [desiredOutPut] = tablefliptrial(angle)
  count = 1;
  for i = angle
      fileID = fopen(['distance',num2str(i),'zenith.plt'],'r'); %open file
      A = fscanf(fileID,'%f',[2 Inf]); %read file
      A=A'; %transpose since not in nx2 
      [uniqVals] = unique(A(:,1)) %find unique values of column one %line 6
      ...
      desiredOutput{count} = [] % write your desired output
      count = count+1;
  end
end

This will return a cell array of desired outputs for each file.

[fernando aguirre]

Thank you, got it all figured out!

[Stephen23]

Always fclose every file that you fopen in the loop!

It is an very bad practice to leave files open like that: continually opening files can eventually cause MATLAB to crash. The MATLAB documentation specifically advises "When you finish processing the file, close it with fclose(fid).".

Always fclose after processing the files!

Answer 2

[Walter Roberson]

Use sprintf or num2str to construct the file name.

[fernando aguirre]

So I changed Overall.m to be

 angle = input('Which angles (degree) are you targeting: ');
 anginput = num2str(angle);
 Tablefliptrial(anginput);

but I am still received with invalid permission