Conditional plotting, changing color of line based on value.
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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.
1 个评论
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????
回答(6 个)
Seth DeLand
2011-2-10
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');
5 个评论
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?
Matt Fig
2011-2-10
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
4 个评论
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.
Matt Tearle
2011-2-11
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
0 个评论
Matt Tearle
2011-2-22
Because I'm a dork, I made a function to do this. It's now available on File Exchange. You can contact me to find out where to send generous tips!
0 个评论
Vieniava
2011-2-10
To control colour of any segment of plot you should use line()
>> doc line
1 个评论
Walter Roberson
2011-2-10
That will not help any more than using plot(). line() has the same limitation, that any one line segment must be a single color.
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