plot a certain x,y values from a large matrix

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smo
smo 2015-8-13
回答： Star Strider 2015-8-13
hi,
i have a 4000rows(with x value from 1:4000) and 2 column (of y values) matrix. How can i plot x&y with, say, taking x value from x > 500 and x<2500 and their corresponding y values?
thank you very much.

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回答（2 个）

Lessmann
Lessmann 2015-8-13
You can use the colon operator to select a subset of your vector, like
plot(x(500:2500),y(500:2500))
  1 个评论
smo
smo 2015-8-13
编辑：smo 2015-8-13
Hi, thanks for that. I didn't make myself clear enough, I actually meant i don't know the index of x. (which means x are a set of numbers not in orders).
But I have did a small test myself and found the answer: first index x-values and then use the x and y value only for that index. I am putting my answer here incase it can help someone else.
for example:
x = [1:10];
y = [11:20];
idx = find (x>3 & x <7);
x_new = x(idx);
y_new = y(idx);
plot (x_new, y_new, '-o')

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Star Strider
Star Strider 2015-8-13
This works:
x = randi(4000, 1, 100); % Create Data
y = randi(99, 2, 100);
xp = x(x>500 & x<2500);
yp = y(:,(x>500 & x<2500));
figure(1)
plot(xp, yp, 'bp')
grid

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