What can I do to make the pattern in the legend larger？I look up a lot of ways, can't solve, ask for help.Thinks!

s1 = scatter(data1(:,2),data1(:,3),900,'o','b','LineWidth',1.5,'MarkerFaceAlpha',.2,'MarkerEdgeAlpha',.2);
scatter(data2(:,2),data2(:,3),900,'d','r','LineWidth',1.5,'MarkerFaceAlpha',.2,'MarkerEdgeAlpha',.2);

%filled
scatter(data1(1:17,2),data1(1:17,3),900,'o','filled','MarkerFaceColor','b','MarkerEdgeColor','b','LineWidth',1.5,'MarkerFaceAlpha',.2,'MarkerEdgeAlpha',.2);
scatter(data2(1:7,2),data2(1:7,3),900,'d','filled','MarkerFaceColor','r','MarkerEdgeColor','r','LineWidth',1.5,'MarkerFaceAlpha',.2,'MarkerEdgeAlpha',.2);
 
set(gca,'xminortick','on');
set(gca,'yminortick','on');
 
lgd = legend({'{\itC_{3v}}(8)',...
    '{\itC_{2v}}(9)', ...
    '{\itC_{3v}}(8)(candidate)',...
    '{\itC_{2v}}(9)(candidate)'}, ...
    'FontSize', 25,'FontName','Times New Roman','Location','northwest','linewidth',2);%'FontSize', 30,
 

[lin]

I can't solve this problem, there is no one who can help me？？

Answer 1

[DGM]

@Star Strider pretty much reviewed what I dug through. There were changes to legend() over the years. A lot of the workarounds seem to rely on using a second output from legend, the use of which has been deprecated over the years and is now no longer documented afaik. The form of the descendant objects changed around R2018b, and then there were more recent changes in the latest versions.

I've tried messing around with the older workarounds based on using the second output from legend(). In R2019b, requesting two outputs from legend() breaks the formatting of the legend icons, namely the alpha -- which is perhaps a complication that simply wasn't revealed in those prior examples.

I chose to solve it using a dirtier approach. This may or may not cause other problems, but it seems stable so far.

% some fake data
n = 100;
x = 1:n;
y = rand(4,n);

% create all the plot objects
marksz = 500;
alpha = 0.5;
marksty = {{'bo'},{'rd'},{'bo','filled'},{'rd','filled'}};
markfa = {0,0,alpha,alpha};
extraparams = {'LineWidth',1.5,'MarkerEdgeAlpha',alpha};
hold on
for k = 1:4
    hsc(k) = scatter(x,y(k,:),marksz,marksty{k}{:}, ...
        'markerfacealpha',markfa{k},extraparams{:});
end

% create the legend object
legstr = {'{\itC_{3v}}(8)',...
    '{\itC_{2v}}(9)', ...
    '{\itC_{3v}}(8)(candidate)',...
    '{\itC_{2v}}(9)(candidate)'};
hleg = legend(hsc,legstr,'FontSize',25,'FontName','Times New Roman', ...
    'Location','northwest','linewidth',2);

% modify properties of undocumented descendant objects
% it may take digging to find the appropriate objects if this changes in the future
legendmarkersz = 15; % new legend icon size
drawnow % make sure the legend is constructed before messing with it
for k = 1:4
    hleg.EntryContainer.Children(k).Icon.Transform.Children.Children.Size = legendmarkersz;
end

Is there a more direct path to find the legend marker object? I don't know. I just dug around until I found something that worked.

[DGM]

FWIW, these are things that I messed with unsuccessfully:

When trying to exploit the 2-output syntax of legend(), the object type used for the legend icon is changed from matlab.graphics.primitive.world.Marker to a simple patch() object. At that point, the face and edge alpha data are lost. While they could be reasserted, patch() objects don't have a simple size property; you'd have to manipulate the vertex list directly. That sounds like a waste of time.

On the other hand, the method using dummy plot objects doesn't seem to actually solve anything as far as I can tell. We can't use plot()/line() objects, since they don't support alpha.

% some fake data
n = 100;
x = 1:n;
y = rand(4,n);

% create all the plot objects
marksz = 500;
alpha = 0.5;
marksty = {{'bo'},{'rd'},{'bo','filled'},{'rd','filled'}};
markfa = {0,0,alpha,alpha};
extraparams = {'LineWidth',1.5,'MarkerEdgeAlpha',alpha};
hold on
for k = 1:4
    hsc(k) = scatter(x,y(k,:),marksz,marksty{k}{:}, ...
        'markerfacealpha',markfa{k},extraparams{:});
end

% create the legend using dummy plot objects with huge markers
legstr = {'{\itC_{3v}}(8)',...
    '{\itC_{2v}}(9)', ...
    '{\itC_{3v}}(8)(candidate)',...
    '{\itC_{2v}}(9)(candidate)'};
legendmarkersz = 15; 
for k = 1:4
    if strcmp(hsc(k).MarkerEdgeColor,'flat')
        thisfc = 'none';
    else
        thisfc = hsc(k).CData;
    end
    hdummy(k) = plot(NaN,NaN,marksty{k}{1},'markersize',legendmarkersz, ...
                    'markerfacecolor',thisfc);
end
hleg = legend(hdummy,legstr,'FontSize',25,'FontName','Times New Roman', ...
    'Location','northwest','linewidth',2);

I know that plot()/line() objects are defined in uint8 RGBA internally, but if I recall, trying to manipulate that directly doesn't work gracefully.

Alternatively, we could make a dummy set of scatter() objects instead, or just use copyobj() to make copies of the scatter objects we already have. The problem I see then is that we still can't actually change the legend icon size any more than we could with the original scatter() objects. We can make them a certain size, but no larger.

figure
% create all the plot objects
marksz = 500;
alpha = 0.5;
marksty = {{'bo'},{'rd'},{'bo','filled'},{'rd','filled'}};
markfa = {0,0,alpha,alpha};
extraparams = {'LineWidth',1.5,'MarkerEdgeAlpha',alpha};
hold on
for k = 1:4
    hsc(k) = scatter(x,y(k,:),marksz,marksty{k}{:}, ...
        'markerfacealpha',markfa{k},extraparams{:});
end

% create the legend using dummy scatter objects with huge markers
legstr = {'{\itC_{3v}}(8)',...
    '{\itC_{2v}}(9)', ...
    '{\itC_{3v}}(8)(candidate)',...
    '{\itC_{2v}}(9)(candidate)'};
legendmarkersz = 99999; % no! bigger!
for k = 1:4
    hdummy(k) = scatter(NaN,NaN,legendmarkersz,marksty{k}{:}, ...
        'markerfacealpha',markfa{k},extraparams{:});
end
hleg = legend(hdummy,legstr,'FontSize',25,'FontName','Times New Roman', ...
			'Location','northwest','linewidth',2);

So with the other workarounds, I don't see a simpler way to get both large markers and alpha.

[lin]

Thank you! This makes me gain a lot.

[DGM]

No problem. It was an interesting exercise.

Answer 2

[Star Strider]

I did a search on this and found How can I change the marker size in legend? and How to set legend marker size among others after my own experiments to do that failed. That does not appear to be possible, although I thought I saw a post a while ago that actually worked, I could not find one that did.

The accepted answer to How to enlarge legend marker size? explains the reason that it is not possible, and offers a work-around.

[lin]

Thank you very much! I will study further.

[Star Strider]

My pleasure!

Answer 3

[Vinay]

Hello Lin

The Legend feature doesn't support direct customization of marker sizes. However, you can work around this limitation by using dummy plots.

These dummy plots can be tailored to achieve the desired legend properties, such as 'marker size', 'Display name', and 'colour'.

It's important to note that the legend marker size will increase only up to a certain point, beyond which it remains constant. The following code demonstrates this approach.

% Set random seed for reproducibility
rng(0);

% RANDOM data
n1 = 30; % Number of data points for data1
n2 = 20; % Number of data points for data2

% Linear trend with some distortion for data1
x1 = linspace(0, 10, n1)';
y1 = 2 * x1 + 5 + sin(x1) + randn(n1, 1) * 0.5; % Linear trend with sine distortion and noise
data1 = [(1:n1)', x1, y1];

% Linear trend with some distortion for data2
x2 = linspace(5, 15, n2)';
y2 = 1.5 * x2 + 3 + cos(x2) + randn(n2, 1) * 0.5; % Linear trend with cosine distortion and noise
data2 = [(1:n2)', x2, y2];

% Plot the data using the given scatter plot commands
ax = axes();
hold on;

% Scatter plots with default marker size
s(1) = scatter(data1(:,2), data1(:,3), 100, 'o', 'b', 'LineWidth', 1.5, 'MarkerFaceAlpha', .2, 'MarkerEdgeAlpha', .2);
s(2) = scatter(data2(:,2), data2(:,3), 100, 'd', 'r', 'LineWidth', 1.5, 'MarkerFaceAlpha', .2, 'MarkerEdgeAlpha', .2);

% Filled scatter plots (subset)
s(3) = scatter(data1(1:17,2), data1(1:17,3), 100, 'o', 'filled', 'MarkerFaceColor', 'b', 'MarkerEdgeColor', 'b', 'LineWidth', 1.5, 'MarkerFaceAlpha', .2, 'MarkerEdgeAlpha', .2);
s(4)= scatter(data2(1:7,2), data2(1:7,3), 100, 'd', 'filled', 'MarkerFaceColor', 'r', 'MarkerEdgeColor', 'r', 'LineWidth', 1.5, 'MarkerFaceAlpha', .2, 'MarkerEdgeAlpha', .2);

% Dummy plots for legend customization
hCopy(1) = plot(nan,nan,'bo','MarkerSize',200,'DisplayName', '{\itC_{3v}}(8)');
hCopy(2)= plot(nan,nan,'rd','MarkerSize',200,'DisplayName', '{\itC_{2v}}(9)');
hCopy(3) = plot(nan,nan,'bo','MarkerSize',200,'MarkerFaceColor', 'b','DisplayName', '{\itC_{3v}}(8)(candidate)');
hCopy(4) = plot(nan,nan,'rd','MarkerSize',200,'MarkerFaceColor', 'r','DisplayName', '{\itC_{2v}}(9)(candidate)');

legend(hCopy,'FontSize',12,'Location', 'northwest', 'linewidth', 2)

Kindly refer to the below documentation of ‘legend’ for more details:

https://www.mathworks.com/help/releases/R2020b/matlab/ref/legend.html?searchHighlight=legend&s_tid=doc_srchtitle