Matlab : put transparancy on a bar plot

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Hello, I have 2 different bar plot on a graph and I would like to put transparancy in order to see all the data even if my curves overlap. I try this code :
b1 = bar(x1,y1);%,'FaceColor',[0.2,0.2,0.5]);
set(get(b1,'Children'),'FaceAlpha',0.3)
hold on
b2 = bar(x1,y1,'FaceColor',[0,0.7,0.7]);
set(get(b2,'Children'),'FaceAlpha',0.2)
But it doesn't work. Also, I would like to calculate the probability of data which are in common between the 2 courb.
Thanks in advance,
Best regards
  1 Comment
pfb
pfb on 28 Apr 2015
what do you exactly mean "it does not work"?
I'm asking because in my case it "sort of works". The bars do become transparent. Only, when they overlap, they produce a different color depending on which one is on top.
I see that you plot y1 vs x1 in both of your plots... But probably you re-define those between the two plots...

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Accepted Answer

Brendan Hamm
Brendan Hamm on 28 Apr 2015
A) The bar series will only have a 0x0 GraphicsPlaceholder as a child (so no properties for the bars Children) B) The barseries does not have a property FaceAlpha (as it is not using the Patch object).
I would suggest a different course of action, and this will depend on the version you are using. We can use x1 and y1 to get back the relative number of counts in each bin.
vals = repelem(x1,y1); % Repeats element of x1(i), y1(i) times (for each i)
In versions >= 2014b we can use this to create a histogram, which will have a Face alpha:
h = histogram(vals);
h.FaceAlpha = 0.2;
Prior versions require us to use hist.
hist(vals,x1) % Hist does not return a handle, but creates an axes with a child of type Patch
patch1 = findobj(gca,'type','Patch'); % The child object of axes is a Patch Object
set(patch1,'FaceAlpha',0.2);
  6 Comments
Brendan Hamm
Brendan Hamm on 7 May 2015
Ok, I made some minor changes.
1. The ptchs return variable is now an array of patches
2. There is a second output ptchGrp which contains an hggroup, which is the way you can group multiple plot objects together. You will need this to change the legend values.
x1 = [-5 -4 -1 3 4 5 6 7 10];
y1 = rand(size(x1));
y1 = y1/sum(y1);
[p1,g1] = createPatches(x1,y1,0.4,'r',0.4);
y2 = rand(size(x1));
y2 = y2/sum(y2);
[p2,g2] = createPatches(x1,y2,0.4,'b',0.4);
Use the hggroup for creating the legend and get second output:
[leg,legIcon] = legend([g1 g2],'Y1','Y2');
legIcon contains the patch objects of the legend
legPatch = findobj(legIcon,'type','patch');
Set the FaceAlpha for the legend's patches:
legPatch(1).FaceAlpha = p1(1).FaceAlpha;
legPatch(2).FaceAlpha = p2(2).FaceAlpha;

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More Answers (2)

Juan Ignacio Bravo Pérez-Villar
Edited: Juan Ignacio Bravo Pérez-Villar on 18 May 2016
Hello, I found a simpler way to do it that works for me on Matlab 2015b
b1 = bar(x1,y1,'r');
b1.FaceAlpha = 0.5;
hold on
b2 = bar(x2,y2,'FaceColor',[0,0.7,0.7]);
b2.FaceAlpha = 0.5;
Hope its useful for somebody.
Regards,
  1 Comment
Qin Liang
Qin Liang on 6 Mar 2017
Works properly and simple on Matlab 2016B

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Chad Greene
Chad Greene on 3 May 2015
This works find for me in 2012b:
x1 = [-5 -4 -1 3 4 5 6 7 10];
y1 = rand(size(x1));
b1 = bar(x1,y1);%,'FaceColor',[0.2,0.2,0.5]); %RXLEV
set(get(b1,'Children'),'FaceAlpha',0.3)
hold on
b2 = bar(x1,y1,'FaceColor',[0,0.7,0.7]);
set(get(b2,'Children'),'FaceAlpha',0.2)
If it's not properly transparent, try
set(gcf,'renderer','opengl')
  1 Comment
Sarah Guiffray
Sarah Guiffray on 5 May 2015
Edited: Sarah Guiffray on 5 May 2015
I do the same but it does not work .. I do not know why. (I have the version R2014b)

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