how to assign a color to individual bars in a bar chart using a colormap based on a separate series of values?

I have the following 10 x 3 matrix:

1 3.43 0.80

2 3.24 0.10

3 3.20 0.60

4 3.15 0.90

5 3.07 0.70

6 2.82 1.00

7 2.76 0.50

8 2.62 0.70

9 2.61 0.60

10 2.55 0.90

I want to plot this as a bar chart using the first 2 columns, but assign colors to each bar based on its value in the 3rd column, using some form of a colormap, such that the color of each bar reflects the value in the 3rd column.

I can get this far easily:

>> x=matrix(:,1);
>> y=matrix(:,2);
>> bar(x,y)

to get this figure, no problem:

But how do I now change the color of each bar based on its corresponding value in the 3rd column of the matrix, using a colormap?

Answer 1

[Monika Phadnis]

You can change color of a particular bar using FaceColor property of bar graph. I followed this documentation example under Data - CData property.

To create a map like object use containers.Map structure. Check this.

%create map of third column values to colors you want
%colors are stored as RGB value matrix 
colormap = containers.Map({'0.1','0.5','0.6','0.7','0.8','0.9','1.0'},{[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]});

b = bar(x,y,'FaceColor','flat');

%this example changes color of first row value in matrix
%get the value of the third column of matrix of first row to map
%get the corresponding RGB value vector of color stored in map
b.CData(1,:) = colormap(string(mat(1,3)))

You can follow similar approach for all row values.

Hope this helps.

[Stephen]

Thanks, Monika. This got me started. And then I found the function "vals2colormap" see https://github.com/vistalab/vistateach/blob/master/cogneuro/tutorial1_timeseries/vals2colormap.m

But I can't seem to get this function to work for me. I keep getting error msg's such as

"Error using horzcat

Dimensions of matrices being concatenated are not consistent."

when I try to create a matrix of RGB values associated with a given colormap, such as the colormap "gray" (64x3 colormap). I have a matrix with say 100 entries (y values) that I want to plot as a bar chart, with each individual bar being color coded according to a separate column of 100 z values. Is the above error telling me I can't get 64 rows of RGB values in the colormap "gray" to concatenate with my 100 entries?

If you or anyone else has an idea how to solve this, please let me know. I'm a relative newbie to MatLab and am struggling to understand plotting.

Answer 2

[Monika Phadnis]

Check the dimensions of the matrices you are concatenating. Since the vals2colormap returns a 100x3 matrix (considering you wanted to map 100 entries), the dimension of y values should 100xsome_value.

Take a transpose or reshape the matrices and try again.

[Stephen]

Thanks again. Got it to work. Am now trying to use that fnx to color individual bars. I appreciate your help.