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Why isn't my color assignment working in this bar graph?

Asked by Shannon on 13 Nov 2013
Latest activity Commented on by Image Analyst on 14 Nov 2013

Hi all, I am trying to assign colors to individual bars in a bar plot that I'm making. I was able to do this before using a 3x3 matrix, but now with the 1x3 matrix (called "Slopes" below) I keep getting the error, "??? Index exceeds matrix dimensions. Error in ==> NColdthree at 93 set(bar1(2),'FaceColor','r')" when I try to run the following script:

Slopes = [-0.002 0.010 -0.012];

subplot(1,3,2) bar1 = bar(Slopes);

%Set the colors of the three bars set(bar1(1),'FaceColor','b') set(bar1(2),'FaceColor','r') set(bar1(3),'FaceColor','g')

%Add legend, axis labels, etc. legend(bar1,'P','E','P-E') ylabel 'Regression Coefficients' xlabel('Northern Cold*') title('Linear Trend','FontSize',16) axis([0 4 -0.05 0.05])

Any thoughts on why I can't specify the colors for the 2nd and 3rd bars? Thanks!

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Shannon

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2 Answers

Answer by Image Analyst on 13 Nov 2013

See attached demo.

4 Comments

Image Analyst on 13 Nov 2013

Let me simplify it by extracting out just the crucial part. You said you want to plot each bar in its own individual color. So I plot each bar one at a time and assign a color to it:

% Plot each number one at a time, calling bar() for each y value.
for b = 1 : numberOfBars
	% Plot one single bar as a separate bar series.
	handleToThisBarSeries(b) = bar(x(b), y(b), 'BarWidth', 0.9);
	% Apply the color to this bar series.
	set(handleToThisBarSeries(b),'FaceColor', barColorMap(b,:));
end

The for loop goes over each bar. For example if you have 10 bars, it iterates 10 times to plot the 10 bars - one bar per iteration.

Next it calls the bar() command to plot the bar. However this bar is plotted using the color from the default color order. (I can change that order if you want and have a demo for that if anyone wants it.) But let's say that the default color is blue and you really wanted purple. So we have to change the bar to purple.

That is what the next line does. The call to set() changes the color of the one single bar that we just plotted to the desired color.

So once I explain it line by line, does it make sense now? The rest of the code is just to set up the colors that you want, and to make the plot look fancy, for example by putting the bar value atop the bar, putting up labels, title, captions, etc.

Shannon on 14 Nov 2013

Great, thank you for the clarification.

Image Analyst on 14 Nov 2013

It sounds like, from your comment to vivek (who's code is the same as mine just with different variable names), that you got it working. If so, please mark my Answer as Accepted, otherwise let's get it figured out.

Image Analyst
Answer by Vivek Selvam on 13 Nov 2013
Edited by Vivek Selvam on 13 Nov 2013

This link says how to. Hope the following illustration helps.

Slopes  = [-0.002 0.010 -0.012];
numBars = numel(Slopes);
x       = 1:numBars;
colStr  = 'rgbymc';
for i = 1:numBars
    barHan = bar(x(i),Slopes(i));
    set(barHan,'FaceColor',colStr(i));
    hold on
end

In case you have a lot of bars (therefore need more colors), you can make use of colormaps ( doc colormap ). For example using jet colormap (replace the corresponding lines in the above code):

colStr = jet(numBars);                 % line 4
set(barHan,'FaceColor',colStr(i,:));   % line 7

1 Comment

Shannon on 14 Nov 2013

Worked like a charm. Thanks.

Vivek Selvam

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