# Plot some part of a correlation matrix

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Yaser Khojah on 10 May 2020
Commented: Tomas Salvadores Viertel on 8 May 2022 at 22:08
I need help please as I have the following correlation matrix, and would like to plot only the lower left part as the upper part is just a mirror of the upper part. As bellow:
I used the following command:
Fields = [1, 4, 5];
Fields_time = Fields +16;
MT_All = rand(100,26);
% MT_All = rand(100,9);
VariableNames={'sigma','sigma','sigma','tau','tau','tau','mNPV'}; % changed to ensure valid syntax
Mat_All_1_4_5 = [MT_All(:,Fields), MT_All(:,Fields_time), MT_All(:,end-1)];
figure
c = corrplot(Mat_All_1_4_5, 'varNames', VariableNames);
% get current figure handle
fh = gcf;
% find x and y label strings that are not empty within subplots
yLabelN = find(cell2mat(arrayfun(@(dIn)~isempty(dIn.YLabel.String),fh.Children,'UniformOutput',false)));
xLabelN = find(cell2mat(arrayfun(@(dIn)~isempty(dIn.XLabel.String),fh.Children,'UniformOutput',false)));
% rename y labels
for ik = 1:length(yLabelN)
if ik <= 3
fh.Children(yLabelN(ik)).YLabel.String = sprintf('\\sigma_{%d}',Fields(ik));
fh.Children(xLabelN(ik)).XLabel.String = sprintf('\\sigma_{%d}',Fields(ik));
elseif ik <=6
fh.Children(yLabelN(ik)).YLabel.String = sprintf('\\tau_{%d}',Fields(ik-3));
fh.Children(xLabelN(ik)).XLabel.String = sprintf('\\tau_{%d}',Fields(ik-3));
else
fh.Children(yLabelN(ik)).YLabel.String = sprintf('m_{NPV}');
fh.Children(xLabelN(ik)).XLabel.String = sprintf('m_{NPV}');
end
end

Mehmed Saad on 10 May 2020
Edited: Mehmed Saad on 10 May 2020
Access all objects with tag 'PlotMatrixScatterAx' using findobj
ax = findobj(fh,'Tag','PlotMatrixScatterAx');
1. Run for loop for all axes and access only thoses axes which have two childrens
2. Access the 2nd's children's Xdata and Ydata ( the scatter which is actually line plot with marker 'o')
3. Save it in Xdata var and do similar for Ydata
4. Now the first children of axes is the line bw two points. access two points Xdata and Ydata which are of size 2. Now interpolate all the Xdata points of children 2 (the scatter) so you can apply threshold. (we have line value for each corresponding Xdata of scatter)
5. then apply condition ( currently) i am accessing points below line and replacing points above line with NaN
6. Replace 2nd children's ydata with new generated ydata
for ii = 1:length(ax)
if(length(ax(ii).Children)>1)
Xdata=ax(ii).Children(2).XData;% scatter Xdata
Ydata=ax(ii).Children(2).YData;% scatter-Ydata
Thdata=interp1(ax(ii).Children(1).XData,ax(ii).Children(1).YData,Xdata);% interpolate limits
ind =Ydata>Thdata;
Ydata(ind) = NaN;
ax(ii).Children(2).YData = Ydata;
end
end
CECILIA STEINWURZEL on 14 Dec 2021
Hi,
any idea on how to plot the Rho on these halved graphs?
thanks!

Jancoba Dorley on 26 May 2020
Hi Yaser, I ran into similar issues and I was able to create a simple fix with help from Matlab tech. See an example with the 'corrplot' data in matLab:
Before (using only corrplot()):
corrplot(DataTable)
Apply the following script:
figure;
[Cr, ~, h] = corrplot(DataTable);
% Find the index to remove the upper triangular part alone, this might
% be different for you base on you data but you can manually import the indexes
% or change the conditions in tril and find
t = tril(Cr, -1) > 0;
mirrors = find(t == 1);
% delete the unnecessary subplots
for i=1:size(mirrors)
delete(subplot(5,5,mirrors(i)));
end
Result
Hope this helps.
Tomas Salvadores Viertel on 8 May 2022 at 22:08
Hello Jancoba, thanks for posting this, it was quite useful!
The code you provided has a little bug when there are negative correlations in the data. Making the following modification fixes the issue.
t = abs(tril(Cr, -1)) > 0;