extract elements and build the remain vector

2020 12 21
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更新时间：2020 12 21
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Hello Community,
i need your help.
A vector v has 128 elements with random numbers.
The elements of index 1 21 31 41 should be etracted, and saved as vector a.
the remain elements of vector v should be saved as vector b.
my version consist two for loops which is in deed a bad solution for large vectors.
PS: the vectors are not constant.
maybe someone could finish the algorithm:
v = 1:128;
a = v([1 21 31 41]);

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Image Analyst
Image Analyst 2020-12-21

2 个投票

Use setdiff():
N = 1600;
v = 1:N;
a = [2 59 87 113]
extracted = v(a)
otherIndexes = setdiff(1:length(v), a);
b = v(otherIndexes)

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David Hill
David Hill 2020-12-21

1 个投票

a=v([1 21 31 41]);
b=v([2:20,22:30,32:40,42:end]);

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Marko
Marko 2020-12-21
编辑：Marko 2020-12-21
Hello David,
thank you for your fast response. I'm sorry for beeing not specfic enough.
Could you develop a code snippet also for non-constant vectors v,a ?
Best,
MJ
David Hill
David Hill 2020-12-21
Depending on what random numbers you want, use rand() or randi() functions (assuming uniform distribution)
v=A*rand(1,128)-B;%generates random numbers between -B:A-B
Marko
Marko 2020-12-21
ok, i see i was not clear enough.
i try beeing a precicsly as possible:
Vector v has N elements:
N = 1600;
v = 1:N;
Vector a is given and contains integer number: e.g.
a = [2 59 87 113]
How could an algorithm extract a from v and save the remaining elements in vector b.
Important: the vectors v and a have not a constant number of elments, they can change.
The solution should be for this example:
b=[1 3 ... 58 60 ... 86 88 ... 112 114 ... 1600]
Marko
Marko 2020-12-21
Perfect!
You are a genius!

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