Adding legend in a plot genereted by a loop

Hello everyone

i have a lot of x,y data sets that i would like to plot. The data sets are stored in a cell structure so that

• DataFiles(1,1) is the first data set i imported
• DataFiles(1,2) is the second
• DataFiles(1,1).data(:,2) is all the y values of the first data set

and so on. the names of the data sets are furthermore stored in OutFiles so that

• OutFiles(1,1).name is the name of the first data set
• OutFiles(2,1).name is the name of the second data set

and so on. because i would like to plot all the x,y data set togehter i wrote a loop. the code is shown below

figure( 'Name', 'Reduced data' );
title('Reduced Raw data')

cc = jet(length(OutFiles)); % creates colormap

% log-lin plot
subplot(2,1,1)
h1 = subplot(2,1,1);
set(h1, 'xscale', 'lin')
set(h1, 'yscale', 'log')
xlabel('Q (Å^{-1})','fontsize',14)
ylabel('Detector counts in 1 sec.')
hold on
for k = 1:length(OutFiles)
    plot(DataFiles{1,k}.data(:,1),DataFiles{1,k}.data(:,2), 'color', cc(k,:)); 
end

+ the other subplot which is just a log-log plot of the same

My problem is that i cannot figure out how i can include the legends in the plot. i have tried include "legend" in the loop so that the loop code becomes

for k = 1:length(OutFiles)
      plot(DataFiles{1,k}.data(:,1),DataFiles{1,k}.data(:,2), 'color', cc(k,:)); 
      legend(OutFiles(k,1)
  end

but this does not work. Simply adding legend(OutFiles) also does not work but OutFiles also contains more information than ".name". i thought about making an array of the names "Legend(1,length(OutFiles))" but i do not know how to make an array of strings. i tried using

>> Legend=zeros(1,10); >> Legend(1,8) = 'test' Subscripted assignment dimension mismatch.

but as you can see i cannot add a string to an array

does anyone have a suggestion on how to add legends to plots made using a loop? any help will be greatly appreciated :)

[mazari ahmed]

l want to make a legend for my figure but l have 3 for loops with three plots like mentioned below : legend 1 : essential legend 2 : less essential legend 3 : most important

for P=1:K
     % body 
  plot(.....,'bo');
  end

      for  Z=N:T
        %body
      plot(....,'ro'):
      end

      for  i=1:L
       %body
      plot(....,'ko'):
      end

how can l manage my legend ? thank you

Answer 1

[Youssef Khmou]

hi, you plot all the data first, and then manipulate the Legend using per example cells as shown below :

 for k = 1:length(OutFiles)
      plot(DataFiles{1,k}.data(:,1),DataFiles{1,k}.data(:,2), 'color', cc(k,:)); 

end

 Legend=cell(2,1)%  two positions 
 Legend{1}=' Your data 1' ;
 Legend{2}=' Your data 2';
 legend(Legend);

In case there are many legends, like N plots, then you do :

 Legend=cell(N,1)
 for iter=1:N
   Legend{iter}=strcat('Your_Data number', num2str(iter));
 end
 legend(Legend)

[Martin Nors Pedersen]

Thank you very much! your solution works and plots the file name when i use

   Legend=cell(length(OutFiles),1);
   for p=1:length(OutFiles)
     Legend{p}=strcat(OutFiles(p,1).name);
   end

it does however give me the warnings messages

Warning: Negative data ignored 
> In is2D at 12
  In legend>make_legend at 333
  In legend at 284
  In SAXSanalysis at 55 
Warning: Negative data ignored 
> In scribe\private\get_legendable_children at 14
  In graph2dhelper at 31
  In legend>make_legend at 347
  In legend at 284
  In SAXSanalysis at 55 
Warning: Negative data ignored 
> In legendcolorbarlayout>doParentResize at 335
  In SAXSanalysis at 59 
Warning: Negative data ignored 
> In legendcolorbarlayout>doParentResize at 335
  In SAXSanalysis at 59

the negatives y-values is a problem because i use log scale for the y-values. this is a separate problem i am working on. i was given these warnings before i emplemented the code for legends

but i cannot understand the other messages i am given. they started to appear when i introduced the code shown above. i can see there is some problem but the warnings do not state a specific problem - they just mention several lines for different matlab functions

[Youssef Khmou]

hi,Martin, good that it worked, but i have no idea about the warning, in the mean time i am sure there is command like " warning off" maybe , it can be used to hide the message .

[Ankit Singh]

Thank you for you help, i am able to use it in a simple script file, but if i try to apply the same in gui i get an error saying "invalid argument" please help. I used the following mentioned code.

      Legend=cell(length(OutFiles),1);
   for p=1:length(OutFiles)
     Legend{p}=strcat(OutFiles(p,1).name);
   end

[Aram Kirakosyan]

Thanks for the solution.

[Nathaniel H Werner]

Is there a way this can be done to skip some entries in the loop? I am making a complicated plot, but only a portion of what is plotted represented actual data. The rest is just for visual aid.

[Carlos Astudillo Gutierrez]

Youssef Khmou! Thanks. You answer worked for me very well!

[Shivam Chopra]

Hi, can you help me in my case??

Thanks in advance

p = (1);
B = [1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3];
figure();
cc = jet(length(B));  %creates colormap

for k = 1:length(B) 
abs_z = diffusion(B(k));
f = (0:10:10^5);
p(k) = plot(log10(f),log10(abs_z), 'color', cc(k,:));
hold on;
end
hold off;

function abs_z = diffusion(B)
t_n = 1E-6;
d_n = 1E+6;
q = 1.6E-19;
m_n = 9.11E-31;
w_c = (q * B)/(m_n);
f = (0:10:10^5);
w = f.*(2*pi);

d_real = 1 + ((t_n^2) * ((w.^2) + (w_c^2))) ; 
d_img = w.*((t_n)*((t_n.^2) * (((w_c.^2) - w.^2)-1))) ; 
d_divider = (1 + ((t_n.^2) * (((w_c.^2) - w.^2).^2)) + ((w.*2*(t_n)).^2)) ;

z = complex(d_real,d_img);
d_m = d_n./d_divider;
abs_z = abs(z).*d_m;
end

[sanjay Negi]

Its a great help changing color at each iteration. Thanks

Answer 2

[Samuel Hammarberg]

When I loop through folders etc. containing data I want to plot, I usually use the 'DisplayName' option.

Example of what my plotscripts typically includes.

% This script plots force vs displacement stored in the Data struct. 
figure, hold on
h = legend('show','location','best');
set(h,'FontSize',12); 

for i=1:length(Data) % Data is a struct containing my data.
        
    x = Data(i).displacement;
    y = Data(i).force;
    name = Data(i).name; % Some text string which i usually take from the folder of each data set in Data.
    plot(x,y,'-x','LineWidth',2,'MarkerSize',2,'DisplayName',name)
    
    
    
end