Legend for multiple lines in Matlab plot

4
votes

I have 13 lines on a plot, each line corresponding to a set of data from a text file. I'd like to label each line starting with the first set of data as 1.2, then subsequently 1.25, 1.30, to 1.80, etc., with each increment be 0.05. If I were to type it out manually, it would be 

legend('1.20','1.25','1.30', ...., '1.80')

However, in the future, I might have more than 20 lines on the graph. So typing out each one is unrealistic. I tried creating a loop in the legend and it doesn't work.

How can I do this in a practical way?

N_FILES=13 ; 
N_FRAMES=2999 ; 
a=1.20 ;b=0.05 ; 
phi_matrix = zeros(N_FILES,N_FRAMES) ; 
for i=1:N_FILES
    eta=a + (i-1)*b ; 
    fname=sprintf('phi_per_timestep_eta=%3.2f.txt', eta) ; 
    phi_matrix(i,:)=load(fname);
end 
figure(1);
x=linspace(1,N_FRAMES,N_FRAMES) ;
plot(x,phi_matrix) ;

Need help here: 

legend(a+0*b,a+1*b,a+2*b, ...., a+N_FILES*b)
5
matlablegend
Why don't you just do x=1:N_FRAMES;? Clearer I think. Actually you don't need x at all, plot(phi_matrix); should work. - yuk
@yuk: That would be better, but they would have to transpose phi_matrix so that it plots each column as a line. - gnovice

5 Answers

7
votes

As an alternative to constructing the legend, you can also set the DisplayName property of a line so that the legend is automatically correct.

Thus, you could do the following:

N_FILES = 13;
N_FRAMES = 2999;
a = 1.20; b = 0.05;

% # create colormap (look for distinguishable_colors on the File Exchange)
% # as an alternative to jet
cmap = jet(N_FILES);

x = linspace(1,N_FRAMES,N_FRAMES);

figure(1)
hold on % # make sure new plots aren't overwriting old ones

for i = 1:N_FILES
    eta = a + (i-1)*b ; 
    fname = sprintf('phi_per_timestep_eta=%3.2f.txt', eta); 
    y = load(fname);

    %# plot the line, choosing the right color and setting the displayName
    plot(x,y,'Color',cmap(i,:),'DisplayName',sprintf('%3.2f',eta));
end 

% # turn on the legend. It automatically has the right names for the curves
legend
6
votes

Use 'DisplayName' as a plot() property, and call your legend as

legend('-DynamicLegend');

My code looks like this:

x = 0:h:xmax;                                  % get an array of x-values
y = someFunction;                              % function
plot(x,y, 'DisplayName', 'Function plot 1');   % plot with 'DisplayName' property
legend('-DynamicLegend',2);                    % '-DynamicLegend' legend

source: http://undocumentedmatlab.com/blog/legend-semi-documented-feature/

5
votes

legend can also take a cell list of strings as an argument. Try this:

legend_fcn = @(n)sprintf('%0.2f',a+b*n);
legend(cellfun(legend_fcn, num2cell(0:N_FILES) , 'UniformOutput', false));
1
votes

The simplest approach would probably be to create a column vector of the numbers to use as your labels, convert them to a formatted character array with N_FILES rows using the function NUM2STR, then pass this as a single argument to LEGEND:

legend(num2str(a+b.*(0:N_FILES-1).','%.2f'));
0
votes

I found this I found through Google:

legend(string_matrix) adds a legend containing the rows of the matrix string_matrix as labels. This is the same as legend(string_matrix(1,:),string_matrix(2,:),...).

So basically, it looks like you can construct a matrix somehow to do this.

An example:

strmatrix = ['a';'b';'c';'d'];

x = linspace(0,10,11);
ya = x;
yb = x+1;
yc = x+2;
yd = x+3;

figure()
plot(x,ya,x,yb,x,yc,x,yd)
legend(strmatrix)