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Tom
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Separate out every fourth element of a Vector

Asked by Tom
on 13 Sep 2019 at 17:57
Latest activity Commented on by Tom
on 13 Sep 2019 at 18:19
I have a 400x1 vector, I essentially need to take the first 3 elements from the vector and put them in a new vector, skip the fourth element, then take elements 5, 6, 7 and skip the eighth, and so on on, until I have a 300x1 vector.
This is slightly more complicated than it sounds, because obviously once you take away an element everything else is going to shift up, so you have to make it clear that this is not the intention.

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2 Answers

Answer by James Tursa
on 13 Sep 2019 at 17:59
Edited by James Tursa
on 13 Sep 2019 at 18:01
 Accepted Answer

V = your vector
result = V;
result(4:4:end) = []; % remove every 4th element
The above syntax with [] on the rhs is special notation for removing the indexed elements on the lhs.

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Answer by Steven Lord
on 13 Sep 2019 at 18:13

If by " so you have to make it clear that this is not the intention." you mean you don't want to delete every fourth element but to replace them with some placeholder, use missing or NaN (if your data is double or single precision.)
A = 1:20;
B = A;
B(4:4:end) = missing
C = A;
C(4:4:end) = NaN
If you want to eliminate every fourth element entirely, use James Tursa's solution.

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Tom
on 13 Sep 2019 at 18:19
Yes, Tursa's method was what I tried before but I thought it was wrong as the code is not producing the right solution, but that method is right it seems so something else must be wrong.

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