Spectral processing: Batch reading of files with co-ordinate data

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Manas M 2020-12-12

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https://ww2.mathworks.cn/matlabcentral/answers/691825-spectral-processing-batch-reading-of-files-with-co-ordinate-data

评论： Alvery 2020-12-15

I have data files with the name "X_Y.txt" where X and Y referes to X(µm),Y(µm) position of spectral files. I have such ~280 files fetched from a rectangular grid, each column in the grid have one such file coded with its X,Y position in the name.

Additional info: Each *.txt file, is 2 columns 2000 rows, contains spectral intensity corresponds to the frequency

Aim: To generate spectral maps (2D map(X-Y),)of specific wavenumber (with ranging intensity)

I have a program, but encounter some issues in the first level(ire, while reading data).

files = dir('*.txt');

Ncurves = length(files);

if Ncurves==0, display('No txt files found!'); return; end

for i = 1:Ncurves,

i

fname = files(i).name;

data = importdata(fname);

if i==0, X = data(:,i); end

Y(:,i) = data(:,1);

dash = strfind(fname,'__');

Xpos(i) = str2num(fname(strfind(fname,'Xµm_')+4:dash(2)-1));

Ypos(i) = str2num(fname(strfind(fname,'Yµm_')+4:dash(3)-1));

end;

save('data.mat', 'Ncurves', 'X', 'Y', 'Xpos', 'Ypos');

return

The error comes when I run

for i = 1:Ncurves,

i

fname = files(i).name;

data = importdata(fname);

if i==1, X = data(:,i); end

Y(:,i) = data(:,1);

dash = strfind(fname,'__');

Xpos(i) = str2num(fname(strfind(fname,'Xµm_')+4:dash(2)-1));

Ypos(i) = str2num(fname(strfind(fname,'Yµm_')+4:dash(3)-1));

end;

While running the entire code I got error messages as

i =

1

Index exceeds array bounds

can someone help me to sort out this issue..

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Manas M 2020-12-13

编辑：Manas M 2020-12-13

Thanks Alvery for looking in to issue with my project

I am a newbe in matlab

The first file is 0_10.txt, I have 7 such files up to 0_17.txt and rest 1_11.text to 16_17.txt.

i tried to run each line the code fails at "Y(:,i) = data(:,1)" and the error is " Unable to perform assignment because the indices on the left side are not compatible with the size of the right side"

Alvery 2020-12-15

I think I can guess the problem. When you make the assignment into Y, the size(Y) will have a value. If size(Y) = [0,0] i.e. it's empty, at the beginning, then no problem it just makes Y big enough to fit the data. If you have already made an assignment to Y, and size(Y) = [8,1] for example, then you load data, and size(data) = [7,2] i.e. it has a different number of rows, then Matlab can't make the assignment Y(:,i) = data(:,1) becasue it doesn't fit.

If you need to capture data with different numbers of rows, you need to use a cell-array. Rather than try to explain cell-arrays here, probably best if you look at the Matlab Doc. https://uk.mathworks.com/help/matlab/cell-arrays.html

Indexing them is a bit more complex. If you have problems with the indexing, a tactic that really helps is to put in a breakpoint just before the problematic line, then use the "evaluate" function or command-line to try out variations of the expression until you find out what works. This isn't a trick you can do in a compiled programming language, and is one of the joys of using an interpreter.

Cheers,

Alvery

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Spectral processing: Batch reading of files with co-ordinate data

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Spectral processing: Batch reading of files with co-ordinate data

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