Adding legend for subplot when none of the subplots include all legend entries

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Catriona 2020-9-29

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评论： LIU 2022-3-21

Hi folks, I am trying to create a subplot where the points are coloured by year, and the years have the same colour in each subplot. Through careful control of the colours I have been able to achieve this, but I only want one legend for the figure, and none of the subplots contain all the years. I cannot figure out (excuse the pun!) how to create just one legend that has all the years (2011-2016). I can easily position one legend at the bottom of the subplot, that's not the problem. Here is the code to make the figure with individual legends (which I don't want in the end) to show you what I mean, along with the code. Thank you!

st_colours=[0, 0.4470, 0.7410;0.8500, 0.3250, 0.0980; 0.9290, 0.6940, 0.1250; 0.4940, 0.1840, 0.5560; 0.4660, 0.6740, 0.1880; 0.3010, 0.7450, 0.9330; 0.6350, 0.0780, 0.1840];
figure15 = figure();
for m=1:12
    subplot(4,3,m)
    if m==1 || m==2 || m==3 || m==4  || m==5 || m==6 || m==8 || m==11  || m==12  %Month
        for r=1:5 %The row this time
        sc(m,r)=scatter(QQG_Amm3M_T_split(m).months.NOAA_ONI(r),QQG_Amm3M_T_split(m).months.mean_Tmelt(r),25,'filled');hold on;
        end
    end
    if m==7 || m==9 || m==10
        for r=1:4 %The row this time
        sc(m,r)=scatter(QQG_Amm3M_T_split(m).months.NOAA_ONI(r),QQG_Amm3M_T_split(m).months.mean_Tmelt(r),25,'filled');hold on;
        end
    end
    if m==11 || m==12 
        for r=1:5 %The row this time
        sc(m,r).MarkerFaceColor=st_colours(r,:);
        end
    elseif m==1 || m==2 || m==3 || m==4  || m==5 || m==6 || m==8
        for r=1:5 %The row this time
        sc(m,r).MarkerFaceColor=st_colours(r+1,:);
        end
    else
        for r=1:4 %The row this time
        sc(m,r).MarkerFaceColor=st_colours(r+1,:);
        end
    end
    legend(string(QQG_Amm3M_T_split(m).months.mean_Year));
    title(Month_labels(m));
    xlim([-2 2.5]);
    ylim([0 1]);
end

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Adam Danz 2020-9-29

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You can simplify the if m==1 || m==2 || m==3 || m.... conditions by using ismember instead.

if ismember(m, [1,2,3, . . .])

Catriona 2020-9-30

That's handy, thanks Adam!!

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Answer 1

Adam Danz 2020-9-29

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https://ww2.mathworks.cn/matlabcentral/answers/602041-adding-legend-for-subplot-when-none-of-the-subplots-include-all-legend-entries#answer_502531

编辑：Adam Danz 2020-9-29

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All you need are the handles to each object you want to include in the legend and the handles can come from different subplots within the same figure. But the legend is a child of only one subplot and can be repositioned relative to that subplot.

% DEMO
figure()
colors = [winter(3);summer(3);autumn(3);copper(3)]; 
subPlotNames = 'ABCD'; 
h = gobjects(3,4); 
for i = 1:4
    ax = subplot(1,5,i);
    h(:,i) = plot([0,1],[.66;.5;.33].*[1,1],'LineWidth',4);
    text([.1,.1,.1],[.66;.5;.33],{'1' '2' '3'},'VerticalAlignment', 'Bottom')
    set(h(:,i), {'DisplayName'}, compose('%s %d',subPlotNames(i),1:3)')
    title(subPlotNames(i))
end
set(h(:), {'Color'}, mat2cell(colors,ones(12,1),3))
lg  = legend(h(:)); 
lg.Position(1:2) = [.8 .3];

This method also works with TiledLayout but requries r2020b for the last line which repositions the legend.

Another method I've used a lot is to use the DisplayName property of line objects to assign the legend string to all line objects within a figure even if the legend string & line line properties associations are redundant (e.g. more than 1 orange marker named "2012"). Then use legendUnq() from the file exchange to eliminate the objects with redundant legend strings. After applying DisplayName, you just need to call this after assigning all objects to the plot,

legend(legendUnq())

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Catriona 2020-9-30

编辑：Catriona 2020-9-30

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Just to say that after a bit of tweaking I was able to use Adam's idea to get one legend with all the entries I needed. The key is to set the display property for every object you create (in my case this was for every month and row of data). Then from the matrix of object properties, I could choose those I wanted in my legend. In my case it was important to set the display year correctly as the sequence of years differed by month, but I understand a lot more about using handles now! Thanks to everyone for all their ideas, I really wasn't sure if this was solveable!!

Here's the code and graph in the end:

%Subplots
st_colours=[0, 0.4470, 0.7410;0.8500, 0.3250, 0.0980; 0.9290, 0.6940, 0.1250; 0.4940, 0.1840, 0.5560; 0.4660, 0.6740, 0.1880; 0.3010, 0.7450, 0.9330; 0.6350, 0.0780, 0.1840];
QQG_years={'2011','2012','2013','2014','2015','2016'};
figure15 = figure();
sc=gobjects(12,6);
for m=1:12
    subplot(4,3,m)
    if m==1 || m==2 || m==3 || m==4  || m==5 || m==6 || m==8 || m==11  || m==12  %Month
        for r=1:5 %The row this time
        sc(m,r)=scatter(QQG_Amm3M_T_split(m).months.NOAA_ONI(r),QQG_Amm3M_T_split(m).months.mean_Tmelt(r),25,'filled');hold on;
        end
    end
    if m==7 || m==9 || m==10
        for r=1:4 %The row this time
        sc(m,r)=scatter(QQG_Amm3M_T_split(m).months.NOAA_ONI(r),QQG_Amm3M_T_split(m).months.mean_Tmelt(r),25,'filled');hold on;
        end
    end
    if m==11 || m==12 
        for r=1:5 %The row this time
        sc(m,r).MarkerFaceColor=st_colours(r,:);
        sc(m,r).DisplayName=QQG_years{r};
        end
    elseif m==1 || m==2 || m==3 || m==4  || m==5 || m==6 || m==8
        for r=1:5 %The row this time
        sc(m,r).MarkerFaceColor=st_colours(r+1,:);
        sc(m,r).DisplayName=QQG_years{r+1};
        end
    else %m==7 or 9 or 10 
        for r=1:4 %The row this time
        sc(m,r).MarkerFaceColor=st_colours(r+1,:);
        sc(m,r).DisplayName=QQG_years{r+1};
        end
    end
    title(Month_labels(m));
    xlim([-2 2.5]);
    ylim([0 1]);
end
f1L=legend(sc([11 23 35 47 59 50]),'Location','SouthOutside','Orientation','Horizontal');
f1P = [0.5 0.02 0.03 0.03];
set(f1L,'Position', f1P,'Units', 'normalized');
%Oh look you can add a subplot title
sgtitle('Quisoquipina Glacier');

LIU 2022-3-21

Thank you very much, this helps me a lot.

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Answer 2

Mario Malic 2020-9-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/602041-adding-legend-for-subplot-when-none-of-the-subplots-include-all-legend-entries#answer_502501

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Legend command is in the loop, therefore it is generated for each subplot. If you want to have it on particular month, you can put this within condition

if m == 1 % Jan
    legend(string(QQG_Amm3M_T_split(m).months.mean_Year));
end

Or you can put it just outside of loop, and legend will be on December.

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Mario Malic 2020-9-29

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Having an additional scatter command for the January, you can have enough entries in the legend, and for it make the legend, but it's not a proper solution.

scatter(nan, nan);

Or maybe you could add an entry to your structure (nan, nan) to December and adjust the code, as it's easier to append the last value rather than the first.

Catriona 2020-9-29