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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.

Arijit
on 5 Mar 2014

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????

Seth DeLand
on 10 Feb 2011

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');

Devendra Moharkar
on 7 Sep 2018

Matt Fig
on 10 Feb 2011

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

Matt Fig
on 10 Feb 2011

Matt Tearle
on 11 Feb 2011

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

Matt Tearle
on 22 Feb 2011

Vieniava
on 10 Feb 2011

To control colour of any segment of plot you should use line()

>> doc line

Walter Roberson
on 10 Feb 2011

MD FAZLE RABBI
on 5 Feb 2017

Hi Matt, If I have several thresholds, how can I plot them ??

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