Scatter 2D plot with specific colorbar

Question

RN 2020-1-31

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评论： Bjorn Gustavsson 2020-2-1

I have three coloumn vectors x, y and z. I have made a scatter plot of x and y with z representing the number of occurrence of 'y' in different colours. See the fig. 1 attached.

Now I need a specific colorbar as shown in fig. 2.

Can anyone help me with the codes in R2014a Matlab.

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Adam 2020-1-31

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You can create a colourmap either manually in code (an nx3 matrix), or using

doc colourmapeditor

for a visual colourmap creation. Then

doc colormap

will apply it to an axes.

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Answer 1

Bjorn Gustavsson 2020-1-31

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编辑：Bjorn Gustavsson 2020-1-31

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You can try something like this:

imagesc % Just to get something to show
axP = get(gca,'position');
% Create axes for colorbar
axCB = axes('position',[axP(1)+axP(3)+ 0.005 axP(2),0.03 axP(4)]);
X = logspace(0,log10(2^11),101)';
pcolor([1 2],X,log10([X,X]))
set(gca,'yscale','log')
shading flat
set(gca,...
    'yaxisLocation','right','ytick',[1:9,10:10:90,100:100:1000 2048],...
    'yticklabel',{'1','','','','','','','','',...
                 '10','','','','','','','','',...
                 '100','','','','','','','','',...
                 '1000','2048'},...
    'tickdir','out',...
    'box','off',...
    'xtick',[])

You might have to doodle a bit with the position of the main axes and the colorbar-axes to get the best layout for your case, and select a suitable colormap.

HTH

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RN 2020-2-1

Fig.jpg

Thanks Bjorn,

It worked this time. Can you help me to set the colours in colourbar as shown in attached image.

From your code I am getting a colour bar which starts with blue and ends with red. But I need the colorbars as shown in the attached fig.

I am trying to get a colorbar which starts with light red>red>orange>yellow>green >blue, in a gradient fashion.

Thanks again.

Bjorn Gustavsson 2020-2-1

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Ramesh, look at the comment from Adam, if you follow his recommendation you will find tools to manually draw a colourmap that fits your needs. You should also make a habit out of searching for solutions on the file exchange, there you will find large number of great solutions to problems - and even if you only find toold that solves 80-90 % of a problem that will only leave you with 10 - 20 % of the work.

One thing to learn is that colormaps in matlab is nothing but n-by-3 double arrays with all elements between 0 and 1. After that you can compose colourmaps in any desired way. If you want to extract the colourmap in the figure you can do something like:

Im1 = imread('fig. 2.jpg');
Cmap_graypinkredorangegreencyanblue = squeeze(mean(Im1(338:-1:20,14:22,:),2));                                         
Cmap_graypinkredorangegreencyanblue = Cmap_graypinkredorangegreencyanblue/max(Cmap_graypinkredorangegreencyanblue(:)); 
imagesc(peaks)
colorbar
colormap(Cmap_graypinkredorangegreencyanblue)

HTH

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