vector3d random sample

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Rick Verberne
Rick Verberne 2020-6-18
评论： Rick Verberne 2020-6-19
Hi all,
I have a problem plotting some data. There are too many points and therefore I want to plot a random sample.
The class is vector3d and contains 13717 points. I would be interested in plotting around a 1000 points or just a certain percentage. However, I keep getting the following error:
'Error using reshape
Product of known dimensions, 3, not divisible into total number of elements, 13717.'
Hope anyone here can help me.
Cheers,
Rick

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回答（2 个）

KSSV
KSSV 2020-6-18
编辑：KSSV 2020-6-18
n = 13717 ; % totalpoints
m = 1000 ; % points to select
x = rand(n,1) ; y = rand(n,1) ; % random data for demo
idx = randperm(n,m) ; % select m points outof n randomly
plot(x(idx),y(idx),'*r') % plot the points selected
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KSSV
KSSV 2020-6-18
Why it din't work? It selects m random points out of n. What did work for you?
Rick Verberne
Rick Verberne 2020-6-19
I think because of the structure of that class, or maybe I just did something wrong. The toolbox allows for sampling when you first load your data. So I created a second dataset. I can use the more detailed information for creating images and calculations on boundaries and use the reduced set for some plots where plotting everything just convolutes the data.

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Ameer Hamza
Ameer Hamza 2020-6-18
编辑：Ameer Hamza 2020-6-18
vector3d is not a MATLAB class. In case you have data points in the form of n*3 matrix. You can do something like this
M = rand(13717, 3); % for example
idx = randperm(size(M,1), 1000); % select 1000 points from 13717
M_small = M(idx, :); % 1000x3 matrix
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Ameer Hamza
Ameer Hamza 2020-6-18
So do you have a custom class vector3d?
Rick Verberne
Rick Verberne 2020-6-19
Yes, or at least the person who wrote it. It is a program called MTEX
https://mtex-toolbox.github.io/vector3d.vector3d.html

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