fname = Sprintf of the file name

I have written a matlab code to read and average certain data in number of files in a folder and write the averaged value back as a file in the same folder. But I am getting some issues in the code.

clear alltopline
close all
clc
n_in = 2;         
n_out = 15362;
N_input = 7;
N_time = 20;
for j=1:N_time
fname = sprintf('vel_xz00%01.f0000',j);
fdata = fopen(fname);   
for i=1:2
    topline = fgetl(fdata);
end
N_tot = (n_out - n_in)*N_input;
Data_tmp = fscanf(fdata,'%f',N_tot);    
fclose(fdata);
for i=1:N_input
    Time(j).Data_sim(:,i) = Data_tmp(i:7:N_tot);
end
end

My files in the folder have the filename as vel_xz0010000 till vel_xz0200000. The code can read the values of the datas from files vel_xz0010000 till vel_xz0090000 but after that cannot read the values from vel_xz0100000 til vel_xz0200000. It gives the following error:

Error using fgets Invalid file identifier. Use fopen to generate a valid file identifier.

Error in fgetl (line 33) [tline,lt] = fgets(fid);

Error in Flow_field_postprocessing (line 16) topline = fgetl(fdata);

Also these files have datas in 15360 X 7 matrix. I want to get the average values of (1,1)element to (15360,7)element of all the files from vel_xz0010000 to vel_xz0200000 and store them as a new vel_xz file with 15360 X 7 elements. Like average of all the (1,1) elements of the 20 files, average of all the (1,2) elements of the 20 files and like so on.

Answer 1

[Stephen23]

The problem is how you are generating the names does not take into account the zeros on the left and right of the non-zero digit. Here are two solutions:

Use dir

It would be easier to use dir and read the filenames from the directory:

S = dir('vel_xz*.f0000');
N = {S.name};
for k = 1:numel(N)
    fid = fopen(N{k});
    ... etc
end

Use fixed length field with leading zeros

If you particularly want to use sprint and generate the filenames yourself, then you need to consider the zeros in the names. In your examples the total number of digits is seven, with leading zeros. This can be created with the correct sprint format string:

for k = 1:20
    sprintf('vel_xz%03d0000',k)
end

displays these strings in the command window:

ans = vel_xz0010000
ans = vel_xz0020000
ans = vel_xz0030000
ans = vel_xz0040000
ans = vel_xz0050000
ans = vel_xz0060000
ans = vel_xz0070000
ans = vel_xz0080000
ans = vel_xz0090000
ans = vel_xz0100000
ans = vel_xz0110000
ans = vel_xz0120000
ans = vel_xz0130000
ans = vel_xz0140000
ans = vel_xz0150000
ans = vel_xz0160000
ans = vel_xz0170000
ans = vel_xz0180000
ans = vel_xz0190000
ans = vel_xz0200000

Averaging matrices

Do not read each file line-by-line, this will be terribly inefficient and slow code. Simply read all of the files into one 3D array, and then the average can be performed with one simple command:

S = dir('vel_xz*.f0000');
N = {S.name};
for k = numel(N):-1:1 % iterate backwards for speed
    M(:,:,k) = importdata(N{k});
end
X = mean(M,3); % take average along third dimension
csvwrite('vel_vx_Average.f0000',M)

[Stephen23]

I tried running this code using MATLAB 2012b using the two attached files, and it worked just fine:

S = dir('temp*.csv');
N = {S.name};
for k = numel(N):-1:1
    M(:,:,k) = importdata(N{k});
end
X = mean(M,3);

I suspect that your file format is not being read correctly. Can you please upload a sample file.

[Stephen23]

Your files have header lines, which need some care when importing into MATLAB. This code will read those two files, and take the mean of each x,y element, as your original question requires:

S = dir('vel_xy*.csv');
N = {S.name};
for k = numel(N):-1:1
    fid = fopen(N{k},'rt');
  tmp = textscan(fid,'%f%f%f%f%f%f','HeaderLines',2,'Delimiter',',');
  M(:,:,k) = cell2mat(tmp);
end
X = mean(M,3);

[Stephen23]

What do you mean "extension"? It is not clear what you want to do. Do you need to identify those files using dir, or create their names using sprint?

[Stephen23]

I recommend that you use dir, to avoid exactly these problems.

You have changed the filename specification from your original question "My files in the folder have the filename as vel_xz0010000 till vel_xz0200000": if you want to use other filenames then you need to change the sprintf format string. The problem is still exactly as I wrote in my original answer: "how you are generating the names does not take into account the zeros on the left and right of the non-zero digit". Did you notice this?

You should learn how the sprintf format string works, it is not at all complicated. Lets have a look at the one I defined earlier:

'vel_xz%03d0000'

The vel_xz is interpreted literally, as are the four 0 at the end of the string (you can change these to match your requirements). Then in the middle we can read this:

'%03d'

This creates a string with three characters with leading zeros and a decimal integer that is the value of the input argument (k, in my answer). If you want to generate those other filenames then you can practice creating different format strings and seeing what effect they have. It is not hard.

Currently your value j is not defined here, so I have no idea what this format string needs to be. Either you need to upload your complete code (and then I can help with the format string), or you read the documentation and learn how format strings work.

[Stephen23]

Did you actually bother to read my comment about changing the format string? You are still using the same format string, even after I explained how you can change it.

You should experiment with this:

for k = 1:100
    sprintf('vel_xz000%03d0',k)
end

Compare the format string from my original answer, and the new one:

'vel_xz%03d0000'
'vel_xz000%03d0'

Perhaps you could read the sprint documentation and try experimenting a little bit with that format string. Your computer will not catch fire if you make a mistake, I promise you.

[Stephen23]

NOTE: The OP deleted all of their comments, but I will leave my responses anyway.

NOTE to OP: Please do not delete your comments and questions. I am not your personal MATLAB tutor, and I am not here to provide you and you alone with solutions to your problems. This is a public forum and our discussion is here to help anyone else who might be interested in the same topic. Because you deleted your comments my responses no longer make much sense, and will not be useful to others reading this forum.

Answer 2

[Marius Mueller]

This might be due to your var fname:

fname = sprintf('vel_xz00%01.f0000',j);

after the xz you have too many zeros to create a file named 'xz0100000'. You want to change this to ever create a fname 'xz0100000'.