饼图着色

Question

I want to create a pie chart without using the command 'pie' in matlab. I have somehow managed but I have failed to color the segments. can someone help me how i can do so: below is my code:

function pie_chart

r = 1;
v = [10 15 20 25 30];

C = ['r' 'g' 'b' 'm' 'c'];

t= 0:0.01:2*pi;

x = r * cos(t);
y = r * sin(t);

plot(x,y, 'k');hold on

for k=1:length(v)

  t=[v/sum(v)*2*pi];

  for t=1:length(t)

    x=[0 r *cos(t)];
    y=[0 r *sin(t)];

    plot(x,y); hold on

    fill(x,y,'C');

  end

  axis square

  axis off

end

Answer 1

There were a few errors in your code:

When you declare C = ['r' 'g' 'b' 'm' 'c']; you concatenate the strings between the [] , so you ended up with C='rgbmc' . It is better to declare it as a cell array, by using the curly braces {} . So your declaration becomes: C = {'r' 'g' 'b' 'm' 'c'};

The fill function needs an enclosed area to fill. You were sending only 2 points coordinates to the function (so basically a line), so it was only coloring the line.

Actually, it wasn't even coloring because you were specifying 'C' as the color. You have to send one of the string contained in your cell array of color: C{k}

Lastly, you do not need a double loop, a single loop over your different quadrant is enough (you were defining t in the outer loop, then immediately overwriting it when declaring the second loop).

The following code produces the colored pie chart. If you do not understand some aspects, I suggest you run it line by line and look at the variable content in the workspace.

function pie_chart

% Define quadrants and color
r = 1;
v = [10 15 20 25 30];
C = {'r' 'g' 'b' 'm' 'c'};

theta = linspace(0,2*pi,359) ;
idx_spokes = round( [1 cumsum(v)/100*length(theta) ] ) ; %// find the indices of the spokes

for k=1:length(idx_spokes)-1

   t = theta( idx_spokes(k):idx_spokes(k+1) ) ;

   x=[0 r*cos(t) 0];
   y=[0 r*sin(t) 0];
   plot(x,y); hold on
   fill(x,y, C{k} );
end

axis square
axis off