# Separate out every fourth element of a Vector

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Tom on 13 Sep 2019
Commented: Tom on 13 Sep 2019
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.

James Tursa on 13 Sep 2019
Edited: James Tursa on 13 Sep 2019
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.

Steven Lord on 13 Sep 2019
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.

#### 1 Comment

Tom on 13 Sep 2019
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.