Plotting while skipping the middle point in a vector

Question

Hieu 2024-7-3，8:16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2134041-plotting-while-skipping-the-middle-point-in-a-vector

评论： Mathieu NOE 2024-7-3，14:55

Hi Matlab Family.

I have to deal with this trouble with my code.

I have a matrix and i need to connect the points in every row. However, when there is a blank between two points ( "blank distance" >1), the code will skip the blank and continue to the end. It is quite easy to solve if i use my code below, draw point to point.

clc

clear all

close all

tic

v = [1 2 3 4 5 8 9 10 20 21 22 30 31 32];

c = [1];

figure()

[QQ,KK]=size(v);

s=1;

for n =1:KK-2;

if v(n+1)- v(n)== 1;

x= [(v(n)),(v(n+1))];

y= [(c(1)),(c(1))];

%data1xy=[x' y'];

plot(x.*s,y.*s,'k')

axis square

ylim([0 2])

xlim([0 35])

%dlmwrite(['n',num2str(n),'.txt'],data1xy,'delimiter','\t');

hold on

elseif v(n+1) - v(n)> 1;

x= [v(n+1),v(n+2)];

y= [c(1),c(1)];

%data1xy=[x' y'];

plot(x.*s,y.*s,'k')

axis square

ylim([0 2])

xlim([0 35])

%dlmwrite(['n_',num2str(n),'.txt'],data1xy,'delimiter','\t');

hold on

end

timeElapsed = toc

The problem is that the code becomes very slow and when the number of rows increases, the point coordinate files that are extracted from the code are too many. So please help to optimize the code by connecting a point to the furthest point as it can while ignoring the middle points. Thanks so much! Have a good day.

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Answer 1

Alan Stevens 2024-7-3，9:57

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https://ww2.mathworks.cn/matlabcentral/answers/2134041-plotting-while-skipping-the-middle-point-in-a-vector#answer_1480531

在 MATLAB Online 中打开

Something like this?

tic

v1 = [1 2 3 4 5 8 9 10 20 21 22 30 31 32];

dv = diff(v1);

ix = find(abs(dv)>1);

v = []; s2 = 0;

for i = 1:length(ix)

s1 = s2+1; s2 = ix(i);

v = [v, v1(s1:s2),NaN];

end

v = [v, v1(ix(i)+1:end)];

c = ones(size(v));

figure()

plot(v,c)

toc

Elapsed time is 0.135112 seconds.

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Alan Stevens 2024-7-3，12:14

在 MATLAB Online 中打开

Do you mean something like this?

v1 = [1 2 3 4 5 8 9 10 20 21 22 30 31 32];
dv = diff(v1);
ix = find(abs(dv)>1);
s2 = 0;
for i = 1:length(ix)
    
    s1 = s2+1; s2 = ix(i);
    v = [v1(s1) v1(s2)];
    filename = ['vfile' int2str(i) '.txt'];
    save(filename, 'v', '-ascii')
    
end
v = [v1(ix(i)+1) v1(end)];
filename = ['vfile' int2str(i+1) '.txt'];
save(filename, 'v', '-ascii')

Hieu 2024-7-3，14:33

My god, it is exactly what i described, amazing. you made my day!

Thanks for your support!!!!

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Answer 2

Mathieu NOE 2024-7-3，11:54

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2134041-plotting-while-skipping-the-middle-point-in-a-vector#answer_1480586

在 MATLAB Online 中打开

hello

if you can avoid update the plot inside the for loop

here I store your data in xx and yy arrays and after the for loop you do the plot

it's more than 10x faster than your original code

also preallocating memory will speed up things especially if you are working with larger arrays (instead of concatenate and make an array grow dynamically in the for loop)

tic

v = [1 2 3 4 5 8 9 10 20 21 22 30 31 32];

c = [1];

[QQ,KK]=size(v);

s=1;

% preallocate memory

xx= zeros(1,2*(KK-2));

yy= xx;

for n =1:KK-2

if v(n+1)- v(n)== 1

x= [(v(n)),(v(n+1))];

y= [(c(1)),(c(1))];

elseif v(n+1) - v(n)> 1

x= [v(n+1),v(n+2)];

y= [c(1),c(1)];

end

% store the results

xx(1,n:n+1)= x;

yy(1,n:n+1)= y;

end

% remove duplicates (optionnal)

[xx,ia,ic] = unique(xx);

yy = yy(ia);

% do one plot call here

figure()

plot(xx.*s,yy.*s,'*k')

axis square

ylim([0 2])

xlim([0 35])

%dlmwrite(['n',num2str(n),'.txt'],data1xy,'delimiter','\t');

timeElapsed = toc

timeElapsed = 0.1244

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Hieu 2024-7-3，14:31

Thanks so much for your suggestion.Absolutely, i will keep it in mind :D

Mathieu NOE 2024-7-3，14:55

my pleasure !

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