how to extract one variable from mat flies
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Dear all, I have one sequence of mat files (1,2, ... 100.mat), each mat file as below: Name Size Bytes Class Attributes
c 1x1 552 struct
data 500x500 2000000 double
timestamp 1x55 110 char
now, I just need the data, would you please tell me how to extract the data from all of the mat files?
Looking forwards your kind help.
Pengju
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Accepted Answer
Image Analyst
on 12 Sep 2014
Edited: Image Analyst
on 12 Sep 2014
myFolder = 'D:\myData';
if ~isdir(myFolder)
errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder);
uiwait(warndlg(errorMessage));
return;
end
% Get list of all .mat files in this folder.
filePattern = fullfile(myFolder, '*.mat');
matFiles = dir(filePattern);
% Go through all mat files, extracting "data" and summing it
% into an accumulation array.
for k = 1:length(matFiles)
baseFileName = matFiles(k).name;
fullFileName = fullfile(myFolder, baseFileName);
fprintf(1, 'Now reading %s\n', fullFileName);
thisData = load(fullFileName);
if k == 1
% Initialize with the first array.
sumOfAllData = thisData.data;
else
% Assume all data arrays are the same size and single or double, not uint8.
% add them together.
sumOfAllData = sumOfAllData + thisData.data;
end
end
5 Comments
Image Analyst
on 12 Sep 2014
Yeah, sorry I forgot to tell you that if you don't accept the output of load() into a variable it "poofs" variables into existence. Generally people don't like that method. If you accept the output into a variable, the variable is a structure with all the internal variables as members/fields of that structure.
More Answers (1)
Robert Cumming
on 10 Sep 2014
You can request the "data" variable explicitly from the file:
load ( filename, 'data' );
Note this will add a new variable "data" to the workspace, so if you load 2 files the second load will overwrite the first, to load multiple files you could do:
files = dir ( '*.mat' );
for ii=1:length(files)
fileData{ii} = load ( files(ii).name, 'data' );
end
If all the "data" are the same size you could save it in a 3D matrix (pre-allocate first).
myMatrix = nan(500,50,100); % pre-allocate with NaN
for ii=1:length(files)
load ( files(ii).name, 'data' );
if exist ( 'data', 'var' ) % this checks to see if data was loaded from the load command.
myMatrix(:,:,ii) = data;
end
clear data % to avoid it being used in the next loop...
end
3 Comments
Robert Cumming
on 11 Sep 2014
How do you plan to put 100 (variable "data") images onto a single image?
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