plot two data sets over different time in the same plot

2013 5 13
2 个回答
7 次查看（30 天）

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Hi,
I have two sets of data, say x = 1:10; y = [0,0,3:10] now I want to plot the data points over time t = 1:10 The thing is I do not want to see the 0-value points of y. or put in another way, I want to plot x over selected time t and y over t2. t2 = 3:10 in this case.
If I directly use y(t2) to add on, then the x axis for that plot will starts from 0, instead of 3 as desired!
Thanks, Howie

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Howie
Howie 2013-5-13
I am asking for two data sets(matrices), not functions. The rules are a little bit different. so if the time has a dimension different than the data, it simply cannot plot. Thanks, Howie

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回答（2 个）

Yao Li
Yao Li 2013-5-13

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plot(t,x)
hold on
plot(t2,y)

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Howie
Howie 2013-5-13
No, you cannot do that to vectors as I believe. x,y are merely matrices.
Yao Li
Yao Li 2013-5-13
I think you'd better give samples of the data points (for example, [1,5,10]) instead of t=1:10.
Howie
Howie 2013-5-13
well, sorry for not phrasing it well. The question is how to plot data points on a selected time period, just as functions. I think there must be a way. Of course your method works well for few points, but I guess not for too many cause it needs human to set things right manually?
Yao Li
Yao Li 2013-5-13
I don't think so. u can add loops for auto-plotting
Howie
Howie 2013-5-13
I am quite a noob so would u mind just show an example of how to do that? I could be deadly wrong on that matter...
Yao Li
Yao Li 2013-5-13
Actually, I'm not quite sure about what you want. For example, t=[t1,t2,t3]; y=[y1,y2,y3]; and each element in t and y is a colunm vector. Make sure the element in t and the corresponding element in y has the same dimention.
for i=1:size(t,2)
hold on
plot(t(:,i),y(:,i))
end
Howie
Howie 2013-5-13
I see. with a loop that should get what I want(with first few elements of y off).
If I understood the algorithm it plots single data point one-by-one
but what if I want piecewise linear line to go through all of the t and y separately?
Yao Li
Yao Li 2013-5-13
The function plot(x,y) plots y vs. x. Thus, no matter what you wanna plot, define the specific x and y.
Howie
Howie 2013-5-13
编辑：Howie 2013-5-13
what I want is x,y in the same plot against t1, but with first few elements of in y:
>> for i=1:size(t1,2)
if i>2
plot(t1(:,i),x(:,i), 'o')
plot(t1(:,i),y(:,i),'o')
else
hold on
plot(t1(:,i),x(:,i),'o')
end
end
Now, the question is how to connect x and y separately...
Yao Li
Yao Li 2013-5-13
Ah, got it!
for i=1:size(t1,2)
if i>2
figure(1)
hold on
plot(t1(:,i),x(:,i), 'o')
figure(2)
hold on
plot(t1(:,i),y(:,i),'o')
else
figure(1)
hold on
plot(t1(:,i),x(:,i),'o')
end
end
Howie
Howie 2013-5-13
for some strange reason there're twp plots jumping out. Also how we connect points with piecewise linear line......
Too late tonight... will reply tomorrow morning... Thanks for all the helps ;) the idea is very good, it's just it can't give me two continuous lines...
Yao Li
Yao Li 2013-5-13
Sorry, I think I misunderstood you for a 2nd time. What did you mean when you said connect x and y seperately? Does it mean you wanna plot a line between each point of x and y?
Howie
Howie 2013-5-13
yes! connecting all thye x; connecting all the y
Yao Li
Yao Li 2013-5-14
connect x to y, or connect a point of x to the next point of x?

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Jakob Sørensen
Jakob Sørensen 2013-5-13

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Here is an example of how it can be done:
t1 = linspace(0,2*pi,100);
t2 = linspace(pi,2*pi,50);
y1 = sin(t1);
y2 = cos(t2);
plot(t1,y1,t2,y2);
Gives you a plot of a sine (y1) and a cosine (y2), where the cosine only exists from pi:2*pi.

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Howie
Howie 2013-5-13
I think it only works for functions, not data points
Jakob Sørensen
Jakob Sørensen 2013-5-13
y1 and y2 are also simply data points. The key thing is the x-axis (t1 and t2). If you try to plot without those, MATLAB won't know when to plot what.
Howie
Howie 2013-5-13
>> x = 1:10; >> y = [0 0 3:10]; >> t1 = 1:10; >> t2 = 3:10; >> plot(t1,x,t2,y) Error using plot Vectors must be the same lengths.
Jakob Sørensen
Jakob Sørensen 2013-5-13
Have a look at your y
>> y = [0 0 3:10];
>> y
y =
0 0 3 4 5 6 7 8 9 10
That means your y vector is 1x10, while your t2-vector (which you use for plotting) is 1x8. So you need to either remove the initial zeros from your y, or make t2 = 1:10.
Howie
Howie 2013-5-13
编辑：Howie 2013-5-13
So here comes the problem. if I just do that, then 0-values of y will be plotted. but all I want is 3:10. I do not think I can do it just by selecting columns since my goal is to remove the points, without changing the position of the points
(I want the first point of y to be(3,3), not (1,3)）.
Maybe I was doing it all wrong.
Yao Li
Yao Li 2013-5-14
so why not just create a new array which stores only the required points?

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Howie
2013-5-13

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