Filling the area in a plot without overlapping

I want to fill the space between lines in a plot and the y=0 line with colour. The code creates three figures, with 3 lines in each figure. The difficulty is, that the lines in each figure are created elsewhere and can be above or below the y=0 line. Additionally, the data is connected, so that the fields belonging to the first line need to have the same colour in all 3 figures. So if y1(1,:) creates a red field in Figure 1, y2(1,:) needs to create a red field in Figure 2 as well. However, it is different data, so in the first figure, the line could be above y=0 and needs to be filled downwards and in the second it could be below and needs to be filled upwards. I tried it like this:

%example vectors (data coming from elsewhere)
c = rand(9,1);
y1 = (-10 + 20 * c(1:3)) .* (0:10).^2;
y2 = (-10 + 20 * c(4:6)) .* (0:10).^2;
y3 = (-10 + 20 * c(7:9)) .* (0:10).^2;


%plot drawing
for k = 1:3
    x = 0:10;
    
    figure
    hold on
    plot(x, y1(k,:), 'r')
    plot(x, y2(k,:), 'b')
    plot(x, y3(k,:), 'g')

    x_fill = [x, fliplr(x)];
    
    y1_fill = [y1(k,:), zeros(1, numel(x)),];
    fill(x_fill, y1_fill, 'r', 'FaceAlpha', 0.1, 'EdgeColor', 'none');

    y2_fill = [y2(k,:), zeros(1, numel(x))];
    fill(x_fill, y2_fill, 'b', 'FaceAlpha', 0.1, 'EdgeColor', 'none');

    y3_fill = [y3(k,:), zeros(1, numel(x))];
    fill(x_fill, y3_fill, 'g', 'FaceAlpha', 0.1, 'EdgeColor', 'none');
end

It almost works, but the colour fields overlap, if there is a line in the middle between another line and the y=0 line. I don't want the colour fields to overlap other fields, but instead stop before the next field starts. Is there a way to do this?

Answer 1

[chicken vector]

You can select the number of plots and curves you want using nPlots and nCurves, respectively.

You can also add more colors using, for example:

colors = {'r','g','b','c','m','y'};

Here's the code:

% Parameters:
nPlots = 3;
nCurves = 3;
colors = {'r','g','b'};

% X Axis data:
x = 0 : 10;
xFill = [x, fliplr(x)];

for j = 1 : nPlots
    
    % Randomise curves:
    c = sort(rand(nCurves,1),'descend');
    y = (-10 + 20 * c) .* (0:10).^2;

    % Create Y coordinates for fill:
    yFillPos = y(c > .5,:);
    yFillNeg = y(c <= .5,:);
    yFill = [y, fliplr([yFillPos(2:end,:); zeros(~isempty(yFillNeg) + ~isempty(yFillPos),length(x)); yFillNeg(1:end-1,:)])];
    
    % Initialise figure:
    figure;
    hold on;

    % Loop over number of curves:
    for k = 1 : nCurves
        plot(x, y(k,:), colors{rem(k-1,length(colors))+1})

        % Fill between curves:
        fill(xFill, yFill(k,:), colors{rem(k-1,length(colors))+1});
    end
end

Result with 50 curves:

Also, a small remark: you can make the code more robust by changing the following lines:

c = sort(rand(nCurves,1),'descend');
...
for k = 1 : nCurves 

Into:

c = unique(sort(rand(nCurves,1),'descend'));
...
for k = 1 : length(c)

[Lukas Schreiber]

Thank you. This is a really good answer, but I explained my question poorly. I updated the question and the code a little bit to make it more clear what I mean.

[chicken vector]

A re-adaption of the previous code to your needs.

Now using colors{idx(k)} makes sure that same y share same colors across plots.

% Parameters:
nPlots = 3;
nCurves = 3;
colors = {'r','g','b'};

% X Axis data:
x = 0 : 10;
xFill = [x, fliplr(x)];

% Randomise curves:
c = rand(nCurves,1,nPlots);
Y = (-10 + 20 * c) .* (0:10).^2;

for j = 1 : nPlots
    
    % Use property of previous code on each figure:
    [csort,idx] = sort(c(:,j),'descend');
    y = Y(idx,:,j);

    % Create Y coordinates for fill:
    yFillPos = y(csort > .5,:);
    yFillNeg = y(csort <= .5,:);
    yFill = [y, fliplr([yFillPos(2:end,:); zeros(~isempty(yFillNeg) + ~isempty(yFillPos),length(x)); yFillNeg(1:end-1,:)])];
    
    % Initialise figure:
    figure;
    hold on;
    
    % Loop over number of curves:
    for k = 1 : nCurves
        plot(x, y(k,:), colors{idx(k)})

        % Fill between curves:
        fill(xFill, yFill(k,:), colors{idx(k)}, 'FaceAlpha', 0.1, 'EdgeColor', 'none');
    end
end