plotting multiple plots in a for loop

I have 34 .txt files with 2 columns (x and y) of data in each, but the length of the columns in each file is variable. (as in one file may be 37x2 and another may be 75x2)

I want to load all the files and then plot them all on the same graph in a for loop. I am able to load the data successfully in the following for loop

for i = 1:34

      filename = ['file',int2str(i),'.txt'];
      load(filename,'-ascii');

end

I tried saving the columns in x and y arrays but I don't think it works because the columns are of different length, the code below is what I added into the for loop

      MTF_filename = ['file',int2str(i)];

      x(i) = MTF_filename(:,1)
      y(i) = MTF_filename(:,2)

the code works but it takes the 1st and 2nd column 1 to 34 times of the string MTF_filename instead of using the array associated with the name file1, file2, file3 etc. so I end up with x = MMMMMMM.... and y = TTTTTTT.... I'm not sure how to fix this and afterwards i'm not sure how to proceed with the plotting.

Answer 1

[Mohammad Abouali]

This part of your code:

for i = 1:34
      filename = ['file',int2str(i),'.txt'];
      load(filename,'-ascii');
end

will result into 34 variables in the memory called, file1, file2, ..., and file34.

The second part of your code that retrieves the value of x,y should be returning characters as its. By the way, based on what you got, I am guessing your real filenames start with MT and not file.

Two options to fix this:

1) using your style of coding: replace

x(i) = MTF_filename(:,1)
y(i) = MTF_filename(:,2)

by

x{i} = eval( [MTF_filename '(:,1)'])
y{i} = eval( [MTF_filename '(:,2)'])

2) change the way you load your file and variables (recommended)

%%some intializations
nFiles=34
filenamePrefix='file';
filenameExtension='.txt';

%%now loading
for i = 1:nFiles
  filename = [filenamePrefix, int2str(i), filenameExtension];
  tmpData=load(filename,'-ascii');
  x{i}=tmpData(:,1);
  y{i}=tmpData(:,2); 
end
clear tmpData;

This would load the x and y of each file into a cell array. each element of x or y would be an array by itself. so x{1} may have 37 elements and x{2} may have 75. You can plot them like this

figure
hold on
for i=1:nFiles
  plot(x{i},y{i},'.')
end

[knifewrench]

Everything worked, thank you so much!

Answer 2

[Joseph Cheng]

in your

      MTF_filename = ['file',int2str(i)];

      x(i) = MTF_filename(:,1)
      y(i) = MTF_filename(:,2)

you're trying to save a Mx1 into a 1x1 index. you should consider using cells as you can store them with varying lengths.

example:

figure,hold on
linecolor = hsv(10);
for i=1:10
  l = randi(10,1,1);
  x{i}=randi(10,1,l);
  y{i}=randi(10,1,l);
  plot(x{i},y{i},'color',linecolor(i,:))
end

Answer 3

[Adam]

Something like this should work if all you want to do is plot the data and not keep all the data for subsequent processing. Then you needn't worry about structures to store different sized columns in.

figure; hold on

for i = 1:34

      filename = ['file',int2str(i)];
      load([filename '.txt'],'-ascii');

      plot( filename(:,1), filename(:,2) );

end

That "plot( filename(:,1), filename(:,2) );" looks a bit silly, but I'm not familiar with loading ascii files and it seems that default behaviour for the syntax you had is for it to simply create a variable in the workspace with the same name as your file.

[knifewrench]

This is something i've already tried and didn't work. I tried it again just then to see what error I get

Error using plot Invalid first data argument

Error in MTF_plotting (line 11) plot( filename(:,1), filename(:,2) );