# Inserting Elements in middle of 1-D, 2-D, N-D Array

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Vijay Anand on 1 Dec 2020
Edited: Ameer Hamza on 1 Dec 2020
Dear All,
I have got an array X = [1 2 3 4 5].
Want to refine the points by averaging neighbours and insert in the middle.
X1 = [1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0].. So, 5 points have become 9 points.
Is there an easier way to do it for a general array?
I would like to make it work in N-dimension also ... for refining the points.
Any help is much appreciated.
K Vijay Anand.

Ameer Hamza on 1 Dec 2020
Edited: Ameer Hamza on 1 Dec 2020
interp1() is suitable for such cases.
X = [1 2 3 4 5];
n_new = 9;
X_new = interp1(linspace(0,1,numel(X)), X, linspace(0,1,n_new))
For a high-dimensional case, you need to specify whether you want to apply it on a single dimension or all the dimensions?
Vijay Anand on 1 Dec 2020
Edited: Vijay Anand on 1 Dec 2020
Thank You Mr.Ameer Hamza.
Amazing Logic !!!
Can you make it work for higher Dimensions also.
X = [
1.0 2.0 3.0
4.0 5.0 6.0
7.0 8.0 9.0
]
becomes,
X1 = [
1.0 1.5 2.0 2.5 3.0
2.5 3.0 3.5 4.0 4.5
4.0 4.5 5.0 5.5 6.0
5.5 6.0 6.5 7.0 7.5
7.0 7.5 8.0 8.5 9.0
]
-Vijay
Ameer Hamza on 1 Dec 2020
Edited: Ameer Hamza on 1 Dec 2020
Try interp2():
X = [
1.0 2.0 3.0
4.0 5.0 6.0
7.0 8.0 9.0
];
new_size = [5 5];
[xg, yg] = meshgrid(linspace(0,1,size(X,2)), linspace(0,1,size(X,1)));
[xg_, yg_] = meshgrid(linspace(0,1,new_size(2)), linspace(0,1,new_size(2)));
X_new = interp2(xg, yg, X, xg_, yg_);
or interpn() for a more general solution.

Stephan on 1 Dec 2020
Edited: Stephan on 1 Dec 2020
This may help
X = [
1.0 2.0 3.0
4.0 5.0 6.0
7.0 8.0 9.0]
F = griddedInterpolant(X)
[xq,yq] = ndgrid(1:0.5:3);
Vq = F(xq,yq)
results in:
X =
1 2 3
4 5 6
7 8 9
F =
griddedInterpolant with properties:
GridVectors: {[1 2 3] [1 2 3]}
Values: [3×3 double]
Method: 'linear'
ExtrapolationMethod: 'linear'
Vq =
1.0000 1.5000 2.0000 2.5000 3.0000
2.5000 3.0000 3.5000 4.0000 4.5000
4.0000 4.5000 5.0000 5.5000 6.0000
5.5000 6.0000 6.5000 7.0000 7.5000
7.0000 7.5000 8.0000 8.5000 9.0000
Vijay Anand on 1 Dec 2020
Thank a lot Mr.Stephan,
Works perfectly fine and solves my requirement !!!
Cheers,
Vijay