Plot several lines with color based on a value in

Question

I have a matrix consisting of 5 columns. The first and second columns are for x_start & y_start of the line, the third and fourth are for x_end & y_end. The fifth is -concentration of contaminant in this line- giving the value for the color of my graph. I want to plot x_start & y_start with x_end & y_end for each line and give this line a color based on the value of concentration which is ranging in color from Cmin to Cmax within a colormap. Any help?

Answer 1

I hope I've understood your question correctly. You can try the following code. Assuming your data is in the following format:

%    x_start y_start x_end y_end concentration
A = [0         0      1      1     0.3
     0         1      3      3     0.6
     3         1      6      2     1.2];

and you use one of the matlab colormaps

cmap = colormap;

Based on a minimum and maximum concentration (first and last value of the colormap) you can calculated to indices of the colors by

con_min = 0;
con_max = 2;
ind_c = round((size(cmap,1)-1)*A(:,5)/(con_max-con_min))+1

and overwrite the ColorOrder of the graph with

figure;
set(gca,'ColorOrder',cmap(ind_c,:),'NextPlot','replacechildren');

and do the plot with

plot([A(:,1) A(:,3)]',[A(:,2) A(:,4)]');

EDIT: To display the correct colorbar, just add

colorbar                  % Display the colorbar
caxis([con_min con_max])  % Scale it to the correct min and max

Answer 2

My approach which is not fully automated (if you expected something like this) would go:

1. Determine the range of the concentration of contaminant meaning the min and max value.
2. Decide how many different plots you want and split your concentration values into the bins.
3. Plot each line by providing an index of the bin each sample belong to.

To give an example:

I usually prefer a combined scheme with varying line style, point style and color

lines = '-:';
points = '<>^vdho';
color = 'rgbkm';

So if a sample falls into 1st bin (imagine i = 1) I will do something like:

i = lines(mod(i,length(lines))+1);
p = points(mod(i,length(points))+1);
c = color(mod(i,length(color))+1);
plot(..., sprintf('%s%s%s', l, p, c));

and since you have a random combination of lines, points and colors the different lines you get are 2*7*5 = 70. Of course you can change the combinations.

I guess maybe @Nemesis's solution might be more elegant but this one gives direct control on some parameters and that's why I provide it.

P.S. I use only these colors because other like cyan ('c') or yellow ('y') do not show really well.