How can I load multiple tiff files through a loop?

I am trying to load multiple tiff files like this:

for i=66:96
    LSTday=strcat('Research\MODIS\MOD11A1\MOD11A1.006_LST_Day_1km_doy20101',string(i));
end

but, I keep getting imread error: Error using imread>parse_inputs (line 450)

The file name or URL argument must be a character vector.

Can anyone kindly help me what is the issue?

[Walter Roberson]

Which MATLAB release are you using? There were a small number of releases after string() was introduced but before imread() recognized it.

[Mery960]

I am using 2018a version

Answer 1

[Image Analyst]

See code samples in the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

Here is code I adapted from it for you:

folder = 'Research\MODIS\MOD11A1\MOD11A1.006_LST_Day_1km_doy20101';
if ~isfolder(folder)
    errorMessage = sprintf('Folder %s does not exist.\n', folder);
    uiwait(errordlg(errorMessage));
    return;
end
% Use fullfile() if you need to prepend some other folder to the base file name.
% Adapt to use which ever cases you need.
for k = 66 : 96
    % Create an image filename, and read it in to a variable called imageData.
    fullFileName = fullfile(folder, sprintf('%d.tiff', k));
    if isfile(fullFileName)
        imageData = imread(fullFileName);
        imshow(imageData, []);
        drawnow;
    else
        fprintf('File %s does not exist.\n', fullFileName);
    end
end

[Mery960]

Thank you. But I got errors as I have a string(i) with each image and that is not read in the loop.

[Stephen23]

"But I got errors as I have a string(i)..."

Your code has errors. Image Analyst's code does not call STRING anywhere.

So far Walter Roberson explained that you cannot use a string with IMREAD. Yet you persist in trying to use a string input to IMREAD. What do you expect to change if you keep doing the same thing?

[Mery960]

I understood that but it is not looping through the image as the last part is changing from 66:96 as in this part LSTday=strcat('Research\MODIS\MOD11A1\MOD11A1.006_LST_Day_1km_doy20101',string(i));

What can I put there instead of a string? the code image analyst shared gives this error:

Researcj\MODIS\MOD11A1\MOD11A1.006_LST_Day_1km_doy20101\96.tiff does not exist. (whereas the data isn't set like this.

[Stephen23]

"What can I put there instead of a string?"

Did you try the suggestions that you have been given so far on this thread?

• CHAR of a string scalar
• SPRINTF of a numeric

Or use DIR, which probably suits your use-case better anyway. See:

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

[Image Analyst]

Actually you should probably use the other method in the FAQ where you just get a list of everything that's definitely there, rather than build up a filename and hope that it's there. But anyway, either way will work, IF you'll just follow the FAQ instead of continuing to try to use your way.

Answer 2

[Walter Roberson]

In R2018a, imread() requires a character vector, not a string() object.

https://www.mathworks.com/help/releases/R2018a/matlab/ref/imread.html?searchHighlight=imread&s_tid=doc_srchtitle#btnczv9-1-filename

The first release that supported string objects for file names was R2018b, the release after you have.

[Mery960]

Is there any other function I can use to read the string file in a loop then? I have way too many data to load.

[Stephen23]

"Is there any other function I can use to read the string file in a loop then?"

Use a character vector rather than a string, just as Walter Roberson wrote.

"I have way too many data to load."

The MATLAB documentation show how to load multiple files. Note that it recommends SPRINTF:

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

[Walter Roberson]

char() of a string scalar gives you a character vector

Answer 3

[Voss]

In place of the code you posted, do this:

file_name_prefix = 'Research\MODIS\MOD11A1\MOD11A1.006_LST_Day_1km_doy20101';
for i = 66:96
    LSTday = sprintf('%s%d',file_name_prefix,i);
end

And use LSTday the same as you are already doing in the rest of the code, e.g., using it in imread().

[Image Analyst]

Except that I think you really meant to use fullfile() which is more robust since it doesn't care if the folder ends with a slash or not - it will always get it right.

[Voss]

Well, I didn't want to assume that 'MOD11A1.006_LST_Day_1km_doy20101' is a directory when it might be part of the file names, e.g., file names might be:

• MOD11A1.006_LST_Day_1km_doy2010166
• MOD11A1.006_LST_Day_1km_doy2010167
• etc.

OP has reported: "Researcj\MODIS\MOD11A1\MOD11A1.006_LST_Day_1km_doy20101\96.tiff does not exist." but that could be for any one of a number of reasons.