Conditional plotting, changing color of line based on value.

Question

S Tajik 2011-2-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1156-conditional-plotting-changing-color-of-line-based-on-value

评论： Devendra Moharkar 2018-9-7

I've got a live stream of data coming to MATLAB. MATLAB does all the calculations and plotting just fine. The only problem is the colour of the plot lines.

I would like to have the plot line change colour automatically when is above or below a set number.

For example if my data is above 0 the plot line would be green and if below 0 the plot line would be red. So after a while when many data points were generated and plotted on the MATLAB figure, I'd like to see all lines above 0 to be green and all lines below 0 in red.

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Arijit 2014-3-5

I like to mark in a stream time series data when data value equals to a threshold. Whenever such value is reached in a streaming time series plot the marker will appear and then streaming will go on with the marker. I have modified code from http://www.mathworks.in/matlabcentral/answers/87466-real-time-plot-from-streaming-data as:

t = 0 ; x = 0 ; startSpot = 0; interv = 1000 ; % considering 1000 samples step = 0.1 ; % lowering step has a number of cycles and then acquire more data while ( t <interv ) b = sin(t)+5; x = [ x, b ]; plot(x) ; if ((t/step)-500 < 0) startSpot = 0; else startSpot = (t/step)-500; end axis([ startSpot, (t/step+50), 0 , 10 ]); grid t = t + step; drawnow; pause(0.01) end

But this is not working as intended????

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Answer 1

Seth DeLand 2011-2-10

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https://ww2.mathworks.cn/matlabcentral/answers/1156-conditional-plotting-changing-color-of-line-based-on-value#answer_1673

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Here's a way to do it that splits the data up into 2 lines and then plots them both. Overlapping points are set to NaN so that they are not plotted.

% Your Data
x = 0:0.01:10;
y = sin(x);
% Level for Color Change
lev = 0.2;
% Find points above the level
aboveLine = (y>=lev);
% Create 2 copies of y
bottomLine = y;
topLine = y;
% Set the values you don't want to get drawn to nan
bottomLine(aboveLine) = NaN;
topLine(~aboveLine) = NaN;
plot(x,bottomLine,'r',x,topline,'g');

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Walter Roberson 2011-2-11

plot(bottomLine,'r');

hold on;

plot(topline,'g')

Devendra Moharkar 2018-9-7

Hi, how can I use this code if i have like 3 thresholds, lets say i have data 0:10 and i want 1:3 to be green , 4:7 to be blue and 8:10 to be red?

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Answer 2

Matt Fig 2011-2-10

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https://ww2.mathworks.cn/matlabcentral/answers/1156-conditional-plotting-changing-color-of-line-based-on-value#answer_1661

在 MATLAB Online 中打开

Perhaps you mean something like this:

x = -10:.01:10;
y = sin(x);
idx = y<=0;
plot(x(idx),y(idx),'r*',x(~idx),y(~idx),'b*')

EDIT

Simulate data coming in one piece at a time. Use a FOR loop as the simulated data retrieval mechanism.

x = -10:.01:10;
for ii = 1:length(x)
      y(ii) = sin(x(ii));  % Data point ii has come in.
      if y(ii)<0
          c = 'r*';
      else
          c = 'b*';
      end
      plot(x(ii),y(ii),c)
      hold on
  end

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S Tajik 2011-2-10

data coming in live (numerical) and then used to do some calculations on it (find the high and low of a certain period).

once the calculations are done all the NEW data are stored in vectors. and feeded into the plot diagram. Ive been trying to use your method to do so but so far nothing. in your example you used y value as a condition, what I need is as follow:

if price>myIndicator

plot price green

if price<myIndicator

plot price red

hope that explains a bit more

thanks for the help.

Matt Fig 2011-2-10

Notice I did not work on the whole vector with an IF statement! When I was working with the whole vector, I used a logical index instead. Look at the idx value in my first post and see how I used it.

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Answer 3

Matt Tearle 2011-2-11

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https://ww2.mathworks.cn/matlabcentral/answers/1156-conditional-plotting-changing-color-of-line-based-on-value#answer_1706

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Maybe this is going overboard, but given your comment "but it only plots dots and do not connect them together", I'm guessing you're getting a lot of crossings of the cutoff value. So... here's a brute-force approach that actually interpolates between the crossings.

Because of what you said about size and memory, I tried to make it so that memory wouldn't be an issue. (So the code isn't as pretty as it probably could be.)

x = 0:0.1:10;
y = sin(4*x);
clr = {'b','r'};
lev = -0.35;
n = length(y);
idx = [0,find(sign(y(2:end)-lev)~=sign(y(1:end-1)-lev)),n];
nidx = length(idx);
for k=2:nidx
    x1 = idx(k-1)+1;
    x2 = idx(k);
    line(x1:x2,y(x1:x2),'color',clr{mod(k,2)+1},'marker','o')
    if k<nidx
        x1 = x2;
        x2 = x1+1;
        y1 = y(x1);
        y2 = y(x2);
        x0 = x1 + (lev-y1)/(y2-y1);
        y0 = y1 + (x0-x1)*(y2-y1);
        line([x1,x0],[y1,y0],'color',clr{mod(k,2)+1})
        line([x0,x2],[y0,y2],'color',clr{mod(k+1,2)+1})
    end
end