One legend for a group of subtightplots

In the following plot, formed by 4 subtightplots, how can I have just one (outside) legend for the left plots, and just one right (outside) legend for the right plots?

addpath('/.../subtightplot');
subplot = @(m,n,p) subtightplot (m, n, p, [0.03 0], [0.04 0.03], [0.06 0.06]);
figure('position',[700 100 1200 1200],'Color',[1 1 1]);
hold on
for i = 1 : 4
    subplot(2,2,i); 
    if i == 1 || i == 3 %%% left plots
        hold on
            t = 0:1:10;
            plot(t,20.*cos(t),'^--','LineWidth',1,'Color','b')
            plot(1:10,(1:10).^2,'^--','LineWidth',1,'Color','k')
            plot(1:10,(1:10).^2.3,'^--','LineWidth',1,'Color','g')
        hold off
    else                %%% right plots
        hold on
            plot(1:10,randi([-50,50],10,1),'o-','LineWidth',1,'Color','r')
            plot(1:10,randi([-50,50],10,1),'o-','LineWidth',1,'Color','m')
            plot(1:10,randi([-50,50],10,1),'o-','LineWidth',1,'Color','y')
        hold off
    end
    legend('Box','off');
end
hold off

This is the my desired result:

Answer 1

[Adam Danz]

That FEX function subtightplot is very useful but since R2019b you can use tiledlayout instead and since R2020b, tiledlayout supports global legend placement.

Here's a demo.

fig = figure(); 
tcl = tiledlayout(fig,2,2,...
    'TileSpacing','none',...        % spacing between tiles
    'Padding','compact', ...        % spacing round perimeter
    'TileIndexing', 'columnmajor'); % index by columns

ax1 = nexttile(tcl);                % generate the next tile/axes
hLeft = plot(rand(20,3)+[0 2 4]);           % return line handles
ax1.ColorOrder = [0 0 1; 0 0 0; 0 1 0];
ax1.LineStyleOrder = '--^';

ax2 = nexttile(tcl);
plot(rand(20,3)+[0 2 4]);
ax2.ColorOrder = ax1.ColorOrder;
ax2.LineStyleOrder = ax1.LineStyleOrder;

ax3 = nexttile(tcl); 
hRight = plot(rand(20,3).*[1 1.2 1.5]);
ax3.ColorOrder = spring(3);
ax3.LineStyleOrder = '-o';

ax4 = nexttile(tcl);
plot(rand(20,3).*[1 1.2 1.5]);
ax4.ColorOrder = ax3.ColorOrder;
ax4.LineStyleOrder = ax3.LineStyleOrder;

linkaxes([ax1,ax2])                 % link left axes limits
linkaxes([ax3,ax4])                 % link right axes limits

legLeft = legend(hLeft);            % create left legend
legLeft.Layout.Tile = 'west';       % put legend in left margin

legRight = legend(hRight);          % create right legend
legRight.Layout.Tile = 'east';      % put legend in right margin

[Sim]

Thanks a lot!! :-)

Just a small doubt... Since I have a code where I use the variable "i" in a for loop and therefore here

subplot(2,2,i) 

How can I still use that variable to indicate the different plots/axes

ax1, ax2, ax3, ax4

?

[Adam Danz]

ax = gobjects(1,4);
for i = 1:4
    ax(i) = nexttile(tcl);
    ...
end

Now, instead of have 4 variables that store the axes handles, you have one 1x4 vector of handles that you can index. For example, instead of

ax1.LineStyleOrder = '--^'; % old

you would write

ax(1).LineStyleOrder = '--^'; % new

[Sim]

Thanks a lot! Really appreciated it :-)

I tried to integrate your solution into my original code, and this is what I got...

% addpath('/.../subtightplot');
% subplot = @(m,n,p) subtightplot (m, n, p, [0.03 0], [0.04 0.03], [0.06 0.06]);
% figure('position',[700 100 1200 1200],'Color',[1 1 1]);
fig = figure('position',[700 100 1200 1200],'Color',[1 1 1]);
tcl = tiledlayout(fig,2,2,...
    'TileSpacing','none',...        
    'Padding','compact', ...        
    'TileIndexing', 'columnmajor'); 

% for i = 1 : 4
%     subplot(2,2,i); 
ax = gobjects(1,4);
for i = 1:4
    ax(i) = nexttile(tcl);
    if i == 1 || i == 2 %%% left plots
        hold on
            t = 0:1:10;
            hLeft(1) = plot(t,20.*cos(t),'LineWidth',1,'Color','b');
            hLeft(2) = plot(1:10,(1:10).^2,'LineWidth',1,'Color','k');
            hLeft(3) = plot(1:10,(1:10).^2.3,'LineWidth',1,'Color','g');
        hold off
    else                %%% right plots
        hold on
            hRight(1) = plot(1:10,randi([-50,50],10,1),'LineWidth',1,'Color','r');
            hRight(2) = plot(1:10,randi([-50,50],10,1),'LineWidth',1,'Color','m');
            hRight(3) = plot(1:10,randi([-50,50],10,1),'LineWidth',1,'Color','y');
        hold off
    end
    % legend('Box','off');
end

ax(1).LineStyleOrder = '--^'; 
ax(2).LineStyleOrder = '--^'; 
ax(3).LineStyleOrder = 'o-'; 
ax(4).LineStyleOrder = 'o-'; 
linkaxes([ax(1),ax(2)])             % link left axes limits
linkaxes([ax(3),ax(4)])             % link right axes limits
legLeft = legend(hLeft);            % create left legend
legLeft.Layout.Tile = 'west';       % put legend in left margin
legRight = legend(hRight);          % create right legend
legRight.Layout.Tile = 'east';      % put legend in right margin

Also, I had to replace this line

if i == 1 || i == 3 %%% left plots

with this

if i == 1 || i == 2 %%% left plots

since it looks like that the sub-plots numbering with tiledlayout is different than with subtightplot.. :-)

[Adam Danz]

Well done! It looks like the data in the upper two axes are identical to the data in the lower two axes. If that's the case, just plot the data on the upper axes and use copyobj to copy the graphics objects to the lower axes.

I refactored your code to demonstrate this suggestion but I did not test it. Please take some time to understand what each line is doing.

% It looks like the data in the upper two axes are identical to the data in the lower two axes.  If that's the case, just plot the data on the upper axes and use copyobj to copy the graphics objects to the lower axes.
fig = figure('position',[700 100 1200 1200],'Color',[1 1 1]);
tcl = tiledlayout(fig,2,2,...
    'TileSpacing','none',...
    'Padding','compact', ...
    'TileIndexing', 'columnmajor');

ax = gobjects(1,4);

% Plot upper left axes
ax(1) = nexttile(tcl,1);
hold on
t = 0:1:10;
hLeft(1) = plot(t,20.*cos(t),'LineWidth',1,'Color','b');
hLeft(2) = plot(1:10,(1:10).^2,'LineWidth',1,'Color','k');
hLeft(3) = plot(1:10,(1:10).^2.3,'LineWidth',1,'Color','g');
hold off

% Plot upper right axes
ax(3) = nexttile(tcl,3);
hold on
hRight(1) = plot(1:10,randi([-50,50],10,1),'LineWidth',1,'Color','r');
hRight(2) = plot(1:10,randi([-50,50],10,1),'LineWidth',1,'Color','m');
hRight(3) = plot(1:10,randi([-50,50],10,1),'LineWidth',1,'Color','y');
hold off

% Copy content from upper left axes to lower left axes
ax(2) = nexttile(tcl,2);
copyobj(ax(1).Children,ax(2))

% Copy content from upper right axes to lower right axes
ax(4) = nexttile(tcl,4);
copyobj(ax(3).Children,ax(4))

% set axes properties for left axes
set(ax([1,2]), 'LineStyleOrder', '--^')
% set axes properties for right axes
set(ax([3,4]), 'LineStyleOrder', 'o-')

linkaxes(ax(1:2))             % link left axes limits
linkaxes(ax(3:4))             % link right axes limits
legLeft = legend(hLeft);            % create left legend
legLeft.Layout.Tile = 'west';       % put legend in left margin
legRight = legend(hRight);          % create right legend
legRight.Layout.Tile = 'east';      % put legend in right margin

[Sim]

Thanks a lot for your additional explanations and inputs :-)

About the "It looks like the data in the upper two axes are identical to the data in the lower two axes. If that's the case", well, in the real case, all the plots have different numbers, and I brought this example as it is, just to make things easier... :-)

Answer 2

[Sim]

I found a way to add "side" legends still using subtightplot (not for grouped plots, but for single plots, that can occur more than once in the same large panel), instead of using tiledlayout. And I compared both codes here following. I have the feeling that subtightplot is still more flexible about the fine and manual adjustments of the spaces (around plots and between plots), if compared to tiledlayout (but this is just an opinion).

% tiledlayout
figure()
tcl = tiledlayout(2,3,...
    'TileSpacing','none',...        
    'Padding','compact');
[X,Y,Z] = peaks(20);

ax = gobjects(1,6);
for i = 1:6
    ax(i) = nexttile(tcl);
    if i == 1 % Tile 1
        hold on
        for j = 1 : 3
            hRight(j) = plot(1:10,randperm(10),'o--');
        end
        hold off
    elseif i == 2 % Tile 2
        contour(X,Y,Z)
    elseif i == 3 % Tile 3
        imagesc(Z);
    elseif i == 4 % Tile 4
        surf(X,Y,Z);
    elseif i == 5 % Tile 5
        plot3(X,Y,Z)
    elseif i == 6 % Tile 6
        hold on
        for j = 1 : 3
            hRight2(j) = plot(1:10,randperm(10));
        end
        hold off
    end
end
% Legend
legLeft = legend(hRight);           % create left legend
legLeft.Layout.Tile = 'east';       % put legend in left margin
legRight = legend(hRight2(1:3));    % create right legend
legRight.Layout.Tile = 'east';      % put legend in right margin

% subtightplot
figure()
addpath('/subtightplot');
subplot = @(m,n,p) subtightplot (m, n, p, [0.01 0], [0.01 0.01], [0.01 0.13]);
for i = 1 : 6 
    subplot(2,3,i);
    if i == 1 % Tile 1
        hold on
        for j = 1 : 3
            hRight(j) = plot(1:10,randperm(10),'o--');
        end
        hold off
    elseif i == 2 % Tile 2
        contour(X,Y,Z)
    elseif i == 3 % Tile 3
        imagesc(Z);
    elseif i == 4 % Tile 4
        surf(X,Y,Z);
    elseif i == 5 % Tile 5
        plot3(X,Y,Z)
    elseif i == 6 % Tile 6
        hold on
        for j = 1 : 3
            hRight2(j) = plot(1:10,randperm(10));
        end
        hold off
    end
end
% Legend
h = legend(hRight);
pos = get(h,'Position');
posx = 0.88;
posy = 0.7;
set(h,'Position',[posx posy pos(3) pos(4)]);
h2 = legend(hRight2);
pos = get(h2,'Position');
posx = 0.88;
posy = 0.2;
set(h2,'Position',[posx posy pos(3) pos(4)]);

[Adam Danz]

Great comparison, @Sim! Thanks for sharing. You're right that subtightplot has greater flexibiliy around spacing. In tiledlayout you can set the TileSpacing and Padding properties to a discrete list of enumerators but subtightplot lets you specify the gap and margins numerically.