Question

I’m trying to make a stacked bar plot that should show how different types of rock are varying with depth. I have generated some fictive lithology series based on some real data and want to present them in a readable way. So now I have this matrix A:

A =

2.0000   65.0000
1.0000   19.5000
2.0000    0.5000
4.0000    1.5000
2.0000   58.0000
4.0000    2.0000
2.0000   22.5000
3.0000    7.0000
2.0000   14.5000
3.0000   12.5000
4.0000    2.5000
2.0000   31.5000
1.0000   20.0000
2.0000   20.0000
1.0000   15.5000
2.0000   66.0000
4.0000    0.5000
2.0000    2.5000
3.0000    8.0000
2.0000   61.0000
1.0000   17.5000
2.0000    8.0000
5.0000   19.5000
3.0000   24.5000

where the first column represents the different rock types and the second column the thickness (in meters) of each lithology layer. And now I want to plot this looking like a core-data log. So each rock type, from 1-5, should have one specific color, and the thickness of each colored bar should represent the thickness of that rock type. How can I achieve this?

Answer 1

Aggregate per type

You can find the total thickness of each rock type by using accumarray:

total_type_thickness = accumarray(A(:,1),A(:,2));

It sums up all values of the second column with equal number in the first column. So for your example data, this returns:

total_type_thickness =

   72.5000
  349.5000
   52.0000
    6.5000
   19.5000

The difficult thing is displaying it as a single stacked bar, you can try using this workaround:

http://www.mathworks.com/matlabcentral/newsreader/view_thread/57304

which leaves you with an empty column, which you can hide by setting the x limits:

bar([total_type_thickness'; zeros(size(total_type_thickness'))],'stacked');
xlim([0.25 1.75])
% add a legend with 'Rock Type <ii>'
legend(arrayfun(@(ii) sprintf('Rock type %d',ii), 1:length(total_type_thickness), 'uni',false));

For now, I haven’t found a better alternative, as matlab won’t stack the bars if you input vector data, it plots the bars separately in that case..

Display all values, same color per type

For plotting all the data (all layers), you can use the same approach, but now set the color data manually with colormap:

N = size(A,1); % number of layers
M = max(A(:,1)); % number of different rock types

bar([A(:,2)' ; NaN(1,N)],'stacked','facecolor','flat');
xlim([0.25 1.75])

cc = jet(M); % create colormap with N different colors
colormap(cc(A(:,1),:)); % pick for each layer, the correct color and use it as a colormap

For easier adding a legend, I’ll add M dummy values to the original data:

bar([NaN(1,M)  A(:,2)' ; NaN(1,N+M)],'stacked','facecolor','flat');
xlim([0.25 1.75])

cc = jet(M); % create colormap with N different colors
colormap(cc([(1:M)' ;A(:,1)],:)); % pick for each layer, the correct color and use it as a colormap

Now the first M elements in the legend will correspond to Rock type 1,2,.. M:

 legend(arrayfun(@(ii) sprintf('Rock type %d',ii), 1:length(total_type_thickness), 'uni',false));