Need help putting multiple values in Legends

I am fitting straight line into the data I have. I have 6 sets of data. My code fits straight line in for each data set. I have created a loop to put all datasets with their fits on top of each other, into a single plot

for N0=1:6
     f = polyfit(T,Nl,1);

     Nfit = polyval(f,T);

     figure(1)
     plot(T,Nl)
     hold on;

     plot(T,Nfit,'--')

     hold on;
     grid on;
  end

Here the data set is (T,Nl) for different values of N0=[1:6]. Now I need to create a legend which can display each line along with its fit. Can anybody help me?

Answer 1

[Mohammad Haghighat]

First of all, you only need one "hold on". You don't need to repeat it after each plot.

You can add the legend after your loop by calling:

legend('description1','description2','description3','description4','description5','description6');

Answer 2

[Giovanni Mottola]

Here I assumed, as it seems from your question, that T is a 1xm vector and that Nl is a 6xm matrix.

First I'd define an empty vector of plot handles (one for each data set):

vec=zeros(1, 6);

Then create once the first figure, add grid and tell MATLAB to keep adding new plots on top of old ones:

figure(1)   %   you put this in the for loop, but there's no need to make these calls more than once
hold on;
grid on;

Now I modify your code as follows:

for N0=1:6
   f = polyfit(T,Nl(N0, :),1);  % in your original code, Nl is not indexed, so I don't really understand how are you fitting different data sets
   Nfit = polyval(f,T);
   plot(T,Nl(N0, :))   %  plot N0-th dataset
   res=findobj(gca,'Type','line');   %  returns handles of all line objects on current axes
   h(N0)=plot(T,Nfit,'--', 'Color', res(1).Color);  % this way the plot I add (fitted values) has the same color of the original data
   vec(N0)=h(N0);  % add current fit line handle to vector of handles
end

The results should now be something like the following figure:

Then, to add labels (but only to the fit lines) use the legend command:

legend(vec, {'line_1', 'line_2', 'line_3', 'line_4', 'line_5', 'line_6'}, 'Location', 'BestOutside')

Now the resulting figure is:

[Ruskin Patel]

I need to distinguish between the data plotted and line fitted in the legend. I am plotting the data with solid line and the fit with dotted line. The legend should show line1 for both data and fit.

Answer 3

[Walter Roberson]

   ph = gobjects(1, 6);
   legs = cell(1, 6);

   figure(1);

   for N0=1:6
     f = polyfit(T,Nl,1);
     Nfit = polyval(f,T);
     ph(N0) = plot(T,Nl);
     legs{N0} = sprintf('set #%d', N0);
     hold on;
     plot(T,Nfit,'--')
     grid on;
   end

   legend(ph, legs);

But I wonder if you are not trying for something closer to

   ph = gobjects(1, 6);
   legs = cell(1, 6);

   figure(1);

   for N0=1:6
     Nl = N{N0};
     f = polyfit(T,Nl,1);
     Nfit = polyval(f,T);
     ph(N0) = plot(T,Nl);
     legs{N0} = sprintf('set #%d', N0);
     hold on;
     plot(T,Nfit,'--')
     grid on;
   end

   legend(ph, legs);

which would require that the 6 datasets be in N{1}, N{2}, ... N{6} .

If you have a cell array of dataset names then you can assign those in place of the way I assigned legs{N0}, such as

    legs{N0} = filenames{N0};

Note: if you are using R2014a or earlier, replace

ph = gobjects(1, 6);

with

ph = zeros(1, 6);

[Walter Roberson]

   N = 6;
If you want both lines to be legend'd, then:

   ph = gobjects(2, N);
   legs = cell(2, N);

   figure(1);

   for N0=1:N
     f = polyfit(T,Nl,1);
     Nfit = polyval(f,T);
     ph(1, N0) = plot(T,Nl);
     legs{1, N0} = sprintf('line%d', N0);
     hold on;
     ph(2, N0) = plot(T,Nfit,'--');
     legs{2, N0} = legs{1, N0};   %if they are to be the same
     grid on;
   end

   legend(ph, legs(:));