# Replacing elements of an array with a vector

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Greggory on 31 May 2011
Edited: Jesús Zambrano on 18 Feb 2019
I know that you can select elements out of a matrix that meet a condition and assign a new value, i.e.
a = [1 2 3 4 5 6 7 9];
a(a>4) = 0;
a
1 2 3 4 0 0 0 0 0
but what if you have a multidimensional matrix? I want to do something similar to the following:
a = [1 2 3 4; 0 0 0 0];
a(a(1,:)==1) = [a b];
a
a 2 3 4
b 0 0 0
The situation is that I have a matrix where the first three dimensions are spatial and then there's a fourth that contains information about the spatial element. Right now, I'm using For loops to check every element and assign a vector [a b c d] to the spatial element. I would like to vectorize this and it's frustrating how easy it is to do this with one scalers, but it doesn't work with vectors.

Laura Proctor on 31 May 2011
Could you show what it is your starting with and what you would like to have as the result?
Matt Fig on 31 May 2011
I agree, make a real simple example of your actual data and show what you want to do. I am reading this as you have something like this:
A = round(rand(3,3,3,3)); % Sample data
and you want to find, say, all instances which match this:
V = squeeze(A(2,3,2,:))
along the fourth dimension and replace it with, say:
[4;5;6]
Is this close to what you want?

Jesús Zambrano on 18 Feb 2019
Edited: Jesús Zambrano on 18 Feb 2019
Hi Greggory,
According to the solution you show, you can get it by doing:
a(:, a(1,:)==1) = [a; b ]
Best regards,
Jesús