How to plot function with different color for different interval?

Question

I have a typical scenario in which there is a Vector X and Vector Y. Vector X contains increasing values, for example X = [1 1 1 2 2 3 4 4 4 4 4]. Vector Y contains real values of same size as X. Im looking to plot Index Vs Y with color change for each different value of X for the corresponding index.

For example, the plot should have color1 for the first 3 values of 1, color2 for the next 2 values of 2, color3 for 1 value 3 and so on.

Can any one help me

Answer 1

Building on Laurent's answer and implementing your "Index vs Y" requirement,

function color_plot(data_vector, color_vector)
styles={'ro','g.','bx','kd'};
hold off;
for i=unique(color_vector)
    thisIdx=find(color_vector==i);
    thisY=data_vector(color_vector==i);
    thisStyle=styles{mod(i-1,numel(styles))+1}; 
    plot(thisIdx,thisY,thisStyle);
    hold on;
end
hold off;

My version also allows arbitrarily large color indices; if you don't have enough styles defined, it just wraps back around and reuses colors.

Update note I had to fix a sign above in the calculation oh thisStyle.

Testing it with

X = [1 1 1 2 2 3 4 4 4 4 4];
Y=rand(size(X))
color_plot(Y,X)

now gives

Answer 2

A plot() function option would be better (and maybe it exists).

Here's a workaround function to do this:

function colorPlot( data_vector, colors_vector)
%PLOTCOL plots data_vector with colors found in colors_vector

Styles=[{'r-'} {'g-'} {'b-'} {'k-'}];


last_off=0;
last_data=0;
for i=unique(colors_vector)
    data_segment=data_vector(colors_vector==i);
    len=length(data_segment);
    if last_off==0
        hold off;
        plot( data_segment, 1:len,char(Styles(i)));
        last_off=len;
    else
        plot([last_data data_segment],last_off:last_off+len,char(Styles(i)));
        last_off=last_off+len;
    end
    last_data=data_segment(len);
    hold on;
end
hold off;
end

Call it this way :

colorPlot(Y,X);